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1. This paper records various observations supplementing, and in some cases correcting previous accounts of the internal structure of the branchial crown in Pomatoceros triqueter, Serpula vermicularis, Hydroides norvegica, Vermiliopsis infundibulum, Salmacina incrustans, Protula intestinum, Spirorbis corrugatus, and Spirorbis militaris. 2. The muscles in the opercular peduncle of Pomatoceros are longitudinal. 3. A single layer of small longitudinal muscle-fibres, of unknown function, has been found on the abfrontal face of the internal branchial and internal peduncular nerves of most of these serpulids. 4. External branchial muscles are well developed in Pomatoceros, reduced in Serpula, Hydroides, Vermiliopsis, and Spirorbis militaris, and apparently absent in Protula and Spirorbis corrugatus. 5. The pinnules of Pomatoceros and Hydroides, like filaments and opercular peduncles, have a double innervation. 6. The internal skeleton of the serpulid crown consists of sheets and strands of connective tissue-fibres and, in the opercula, of a cartilage-like tissue with a ground substance giving the staining reactions of collagen. The serpulid branchial skeleton is compared with that of sabellids, and the chemical nature of these skeletons is discussed. 7. Extensions of the prostomial and peristomial cavities accompany the branchial blood-vessels into the base of the crown, but have no connexion with the cavities in the branches of the crown. The arrangement of the latter is described. The nature of all these cavities, whether coelomic or blastocoelic, is obscure. 8. The ‘palps’ of Pomatoceros, Serpula, Hydroides, and Vermiliopsis closely resemble pinnules. The blood-vessel and nerve of the ‘palp’ of Pomatoceros are branches of those in the adjacent filament. It is suggested that the serpulid ‘palp’ is a modified pinnule.

1. The early events of sperm entry in Saccoglossus and Hydroides are described and examined in relation to present knowledge of the acrosome reaction and of egg membrane lysins. In Saccoglossus and several other species these events occur in two phases. First. The acrosome filament of the spermatozoön spans the egg membrane barriers, reaches the reactive egg protoplasm, and causes the egg to begin its fertilization reaction. Second. The filament and its connected sperm head move through the egg membrane barriers and enter the egg proper. The first phase is completed in a matter of seconds but the second phase usually requires several minutes. 2. The peripheral areas of the eggs of the two species differ as seen in sections. In Hydroides, but not in Saccoglossus, the vitelline membrane is bounded by a distinct outer border layer of small concentrically differentiated bodies and penetrated by microvilli from the egg. 3. The acrosome filament, seen in the living condition as a delicate thread in Hydroides and as an exceedingly tenuous thread in Saccoglossus, appears to be tubular in both species when seen in electron micrographs of thin sections. 4. The acrosomal region of Hydroides appears to consist of two components—a peripheral one, which may collapse during the acrosome reaction, and a central one related to the acrosome filament. 5. Deliberately induced polyspermic material was used to increase the probability of finding examples of sperm penetration in thin sections. 6. As seen in sections, areas of low electron density, interpreted as spaces or pits from which the material of the membrane is absent, surround the attached or penetrating spermatozoa. (a) In Hydroides the spaces vary greatly in many characteristics including shape, position in the membrane, and size with relation to the enclosed sperm head. In one specimen a portion of the membrane is missing from border to border; no spermatozoön is seen but immediately beneath the space is the apex of a fertilization cone. (b) In every case in which a determination could be made, the spermatozoön in the membrane has undergone its acrosome reaction. (c) In Saccoglossus some pits are found with which several spermatozoa are associated. Generally, where the spermatozoa are more numerous the pit is larger. (d) Pits similar to those seen in Saccoglossus sections are observed in living eggs. They remain in Membrane I after sperm entry. (e) From the above and other considerations it is suggested that the pits and spaces are formed by local action of a lysin or lysins emanating from the individual spermatozoön at the site of sperm entry. 7. It is considered that the suggested lysin would participate in sperm entry by eroding the membrane barrier in the vicinity of the sperm head, thus permitting the sperm head to pass through the membrane. Since the acrosome filament much earlier stimulates the egg's initial fertilization response, this lysin would facilitate the second phase of the early events of sperm entry.

Calcium carbonate, in a finely granular form, is secreted into the fold of the peristomial collar by a pair of tubulo-racemose glands in the peristomium. Most of the organic material of the tube is secreted by the ventro-lateral epithelial cells which surround the main ducts of the calcium-secreting glands. These cells are always filled with a basiphil mucigen which contains some free a-glycol groups. This material retains its affinity for basic dyes and for ferric iron at a low pH. The affinity for iron is retained when the pH is low enough to exclude carboxyl and phosphoric acid groups from the reaction and it is probable that the sulphuric acid groups are responsible. The reactions of this mucigen to histochemical tests together with the similarity in behaviour of a precipitated heparin preparation make it likely that the material is a sulphomucopolysaccharide.

In the polychete Hydroides norvegica there are two opercula with different degrees of organization: one is completely developed and functional, the other, present only in rudimentary outline. The latter only begins to develop when the functional operculum is removed. It was observed that in the whole body of the Hydroides, but particularly in the functional operculum, there is a substance which inhibits the development of the rudimental operculum. This substance was purified in order to determine its chemical nature. From preparation of opercular homogenates we chemically separated numerous fractions, each of which was tested for inhibitory activity and chemical and physical properties. The inhibitor under study proved to be soluble in aqueous solutions, heat resistant, of low molecular weight, of an organic nature, anionic and aromatic. Finally it was chromatographically identified as 5′ adenosine monophosphate.

Twenty-four species of polychaetes settled on test blocks suspended at 13 stations in Los Angeles–Long Beach harbors in 1950–51. Polydora limicola, Capitella capitata, and Hydroides pacificus were the three most frequently occurring species. Although a peak in settling occurred during the spring months, in general, the warmer the water, the greater the number of species present. However, H. pacificus possessed a summer-full peak, and C. capitata exhibited no apparent peak. Many of the species reproduced throughout the year, as indicated by settlement data. A suppression in the number of species was observed whenever the dissolved oxygen concentration was below 4.0 mg/liter.

Previous electron microscope studies indicated that the individual spermatozoön of Hydroides hexagonus forms a hole in the vitelline membrane by means of lysis. Other observations established that the hole is real, being visible in living material during sperm entry. During the present investigation sea water extracts from frozen-thawed sperm were tested for lytic effect on the membrane. In normal living eggs the membrane appears as a single thick envelope, but in electron micrographs of sections it is seen to consist of a narrow outer border layer, a wide principal or middle layer, and a narrow inner border layer. After immersion in sperm extract the outer border layer elevates but does not dissolve, the middle layer liquefies and disappears, and the inner border layer seems not to change. This is interpreted as lysis of the middle layer. The extract exerted the same effect on fertilized and unfertilized eggs. In electron micrographs the sections treated with extract greatly resemble that part of the membrane which has been penetrated by the individual spermatozoön. It is concluded that the individual spermatozoön, too, exerts a lytic effect. Together, the present and two earlier studies are considered clearly to demonstrate that in Hydroides the individual spermatozoön does indeed make an entry hole in the egg membrane by applying lytic material to that part of the membrane in its own vicinity.

As a serpulid, Pomatoceros triqueter L. realises to the highest degree the adaptation to a sedentary life. The calcareous tube in which this annelid lives is characterised by a keel running along its upper surface. It is rather misleading to say that this tube is triangular in section. Figure 2 shows a newly formed calcareous rod; it is spur-shaped; the two rami of the spur might approach each other so nearly as to simulate an almost complete tube. The substratum in this species not only serves as a support, but completes the tube. This is in accordance with the fact that the tubes of Pomatoceros never extend freely off the support as happens with tubes of other serpulids–Protula, for instance. The aim of this paper is to record some observations on the way an adult Pomatoceros endeavours to build a new calcareous tube if it is artificially removed from its old one. I undertook this observation as original work at Roscoff, where a complete literature was not available. I discovered later that Harms, in the course of his research on regeneration in Hydroides pectinata, arrived at identical results. My paper cannot therefore pretend to more than a confirmation of previous results.

Electron micrographs of inseminated eggs of Hydroides hexagonus previously had shown that in the immediate vicinity of the penetrating spermatozoön a small portion of the vitelline membrane regularly was absent, and it had been suggested that this area was a hole made by lytic activity of the individual spermatozoön during the course of its passage through the membrane. This deduction would receive support if it could be established that a sperm entry hole does form in living material. During the present study a hole repeatedly observed and photographed in the membrane of living eggs was found to arise as the spermatozoön penetrated the membrane. Gently compressed eggs formed exovates only through this hole. The holes, and exovates, were not found except at sperm entry sites. It was concluded that this hole is the counterpart of the area from which the membrane is absent in the electron micrographs cited above, and that the spermatozoön makes this hole. In an electron micrograph two spermatozoa which had penetrated the membrane at separate but closely neighboring points now occupy a single hole. It is argued that if each spermatozoön had displaced the membrane mechanically to make its hole, then there should be two holes, with a partition of membrane between them, but if each had eroded the membrane by applying lysin, a single hole should have formed as the eroded areas expanded and finally merged into one. The latter view agrees with the facts of the electron micrograph. It is concluded that lysis is the most probable means by which the individual spermatozoön makes its hole.

The comparative toxic tolerance of several fouling organisms was based on the sequence of their attachment to copper and mercury antifouling paints. A red alga, Polysiphonia sp., and the barnacle, Balanus amphitrite, were the most tolerant and attached to copper and mercury paints before other organisms. The encrusting bryozoan, Watersipora cucullata, was found to be slightly more tolerant to copper but considerably less tolerant to mercury than the above two forms. Less tolerant forms were Balanus improvisus, Hydroides parvus, Bugula neritina, Anomia sp., Enteromorpha sp., tunicates and hydroids. Other species, though attaching to nontoxic surfaces, were never found on the toxic paints.

(1) The surface precipitation reaction has been obtained in the eggs of fifteen marine animals. (2) The reaction assumes a characteristic form for each species. (3) Two general types of reactions occur. One which is accompanied by breakdown of some type of protoplasmic granule (as inArbacia, Asterias, Echinarachnius, Cerebratulus andNereis). The other, in which there is no disintegration of granules (Gonionemus, Phascolosoma, Amphitrite, Hydroides, Chaetopterus, Cumingia, Mytilus, Chaetopleura andPodarke). (4) The presence of calcium is a necessary requisite for the reaction.

Segmentation results in a round blastula with a very reduced blastocele. Invagination produces at first an almost spherical gastrula. But this soon begins to assume the conical shape of the early trochophore. The blastopore, which is small, closes from behind forwards, the anterior portion remaining as the mouth, while the posterior closes completely, the anus breaking through immediately at this point. The blastopore, which was originally ventral, becomes shifted to a ventro-lateral position. At a time when gastrulation is about half completed, some cells appear on either side of the endoderm and take up a bilateral position. They probably correspond to the lateral portions of the larval or ectomesoblast of Thalassema. They subsequently form the head-kidneys in Eupomatus. At the same time two conspicuous cells are usually distinguishable in the ventral lip of the blastopore. These are the cœlomesoblast cells. In the further progress of invagination, they are carried inwards in the wall of the archenteron, finally coming to lie in the anal end of the gut. Here at a considerably later stage they give rise to the mesoderin bands. There is a short stage in the early trochophore when the head-kidneys are already functional while the mesoderin bands are alone represented by these two cells in the gutwall. With the formation of the bands the organisation of the trochophore is completed. The bauds during their growth are never seen to bud off cells into the blastocœl. They remain from the first a compact mass of cells clearly distinguishable from the irregular cells of the ectomesoblast and the head-kidneys. The head-kidneys open into the proctodasura. They are formed from the ectomesoblast.

Anomalous individuals in five species of marine polychaetes are described. The anomalies fall into three structural types, viz, duplication, bifurcation and common variation. Included in the first are double ventral cirrus in Perinereis nuntia vallata and duplicate operculum in Hydroides homoceros. Bifid antenna in Lysidice collaris and forked anal papilla in Armandia leptocirris constitute the second type. The third includes supernumerary eyes in Arabella iricolor iricolor and variations in opercular crown in, again, Hydroides homoceros.

ELECTRON microscopy has provided evidence for a series of anatomically distinct stages in the process of fertilization. In the polychaete worm Hydroides hexagonus, Colwin and Col win1,2 have described how production of the acrosome filament is followed by fusion of the gamete membranes and passage of the male pronucleus into the egg cytoplasm. Apart from this anatomical description, little is known of the early stages of fertilization. We now present kinetic evidence for at least one intermediate stage in the fertilization of sea urchin eggs.

The boron isotope composition (δ11B) of marine biogenic carbonates has been predominantly studied as a proxy for monitoring past changes in seawater pH and carbonate chemistry. However, a number of assumptions regarding chemical kinetics and thermodynamic isotope exchange reactions are required to derive seawater pH from δ11B biogenic carbonates. It is also probable that δ11B of biogenic carbonate reflects seawater pH at the organism's site of calcification, which may or may not reflect seawater pH. Here, we report the development of methodology for measuring the δ11B of biogenic carbonate samples at the multi-collector inductively coupled mass spectrometry facility at Ifremer (Plouzané, France) and the evaluation of δ11BCaCO3 in a diverse range of marine calcifying organisms reared for 60 days in isothermal seawater (25 °C) equilibrated with an atmospheric pCO2 of ca. 409 µatm. Average δ11BCaCO3 composition for all species evaluated in this study range from 16.27 to 35.09 ‰, including, in decreasing order, coralline red alga Neogoniolithion sp. (35.89 ± 3.71 ‰), temperate coral Oculina arbuscula (24.12 ± 0.19 ‰), serpulid worm Hydroides crucigera (19.26 ± 0.16 ‰), tropical urchin Eucidaris tribuloides (18.71 ± 0.26 ‰), temperate urchin Arbacia punctulata (16.28 ± 0.86 ‰), and temperate oyster Crassostrea virginica (16.03 ‰). These results are discussed in the context of each species' proposed mechanism of biocalcification and other factors that could influence skeletal and shell δ11B, including calcifying site pH, the proposed direct incorporation of isotopically enriched boric acid (instead of borate) into biogenic calcium carbonate, and differences in shell/skeleton polymorph mineralogy. We conclude that the large inter-species variability in δ11BCaCO3 (ca. 20 ‰) and significant discrepancies between measured δ11BCaCO3 and δ11BCaCO3 expected from established relationships between abiogenic δ11BCaCO3 and seawater pH arise primarily from fundamental differences in calcifying site pH amongst the different species. These results highlight the potential utility of δ11B as a proxy of calcifying site pH for a wide range of calcifying taxa and underscore the importance of using species-specific seawater-pH–δ11BCaCO3 calibrations when reconstructing seawater pH from δ11B of biogenic carbonates.

The postcranial morphology of the extremely long-necked Tanystropheus hydroides is well-known, but observations of skull morphology were previously limited due to compression of the known specimens. Here we provide a detailed description of the skull of PIMUZ T 2790, including a partial endocast and endosseous labyrinth, based on synchrotron microtomographic data, and compare its morphology to that of other early Archosauromorpha. In many features, such as the wide and flattened snout and the configuration of the temporal and palatal regions, Tanystropheus hydroides differs strongly from other early archosauromorphs. The braincase possesses a combination of derived archosaur traits, such as the presence of a laterosphenoid and the ossification of the lateral wall of the braincase, but also differs from archosauriforms in the morphology of the ventral ramus of the opisthotic, the horizontal orientation of the parabasisphenoid, and the absence of a clearly defined crista prootica. Tanystropheus hydroides was a ram-feeder that likely caught its prey through a laterally directed snapping bite. Although the cranial morphology of other archosauromorph lineages is relatively well-represented, the skulls of most tanystropheid taxa remain poorly understood due to compressed and often fragmentary specimens. The recent descriptions of the skulls of Macrocnemus bassanii and now Tanystropheus hydroides reveal a large cranial disparity in the clade, reflecting wide ecological diversity, and highlighting the importance of non-archosauriform Archosauromorpha to both terrestrial and aquatic ecosystems during the Triassic.

Hydroides norvegica larvae were reared to settling in 8-10 days at 20°C. The paired conical processes on the collar setae characteristic of the genera Hydroides and Serpula were developed in the larvae by the sixth day. Settling differed from that recorded for other larvae in that (i) larvae could become attached to surfaces comparatively early in their free-swimming life, (ii) "searching" behaviour followed by settling on a particular locus was not observed, (iii) feeding continued through metamorphosis. The primary operculum of the young worm was formed by modification of the third branchial filament of the left side. Certain identification as H. norvegica could not be made until this had been shed and replaced by a secondary operculum developed from the right side 4-8 weeks after metamorphosis.

(1) The asymmetrical development in Hydroides opercula is due to the growth difference between two sides in the same kind of organs. The presence of a functional organ holds its mate in check. Therefore, taking off the functional operculum results in the development of the rudimentary side. (2) This phenomenon of compensatory regulation cannot be considered to be brought about by a nervous reflex set in motion by the stimulation of damaged nerves in the operated operculum, since, for example, the inhibitory influence to a certain extent depends on the degrees of injury. (3) It is also not proved to be due to the production of a certain chemical substance which stimulates the rudimentary organ to grow, while the wound itself affects directly the inhibitory action of the functional operculum. (4) The inhibitory influence is only localized in the operculum and not outside of it. Therefore, cutting off the gill filaments or other parts of the body does not bring a reversal of asymmetry. (5) Within the limit of the operculum there is no special centre of the inhibitory influence, which depends on the intactness of the internal constitution of the organ. Those peripheral parts outside the limit of direct blood supply can be cut off, without the resulting reversal of asymmetry. A simple puncturing with a fine needle also has no effect. But greater injury accompanied by an outflow of blood always starts the rudimentary organ developing. (6) The functional operculurn has no regenerative capacity, while the rudimentary one still has. The injured operculum is thrown off sooner or later from the body, and a new start repeats from the beginning the original development. By accelerating this regenerative development of the old functional organ, or properly controlling the growth of the rudimentary organ on the opposite side, a symmetrical animal with two large opercula can easily be derived. On the other hand, if both rudiments antagonistically check each other's development, a symmetrical animal with two small rudimentary opercula is produced. (7) Since, however, either the right or the left or even both rudiments can be made to develop into a functional organ, the inhibitory influence must act at first on both alike, unless a threshold value is assumed. In the present species of Polychsete it is as a rule the right-handed one that grows more quickly than the other. (8) With regard to the nature of the asymmetry in Hydroides it seems to be quite different from that in the male Gelasimus in which the asymmetry of the chelas is said to be derived from the symmetrical condition relatively late in development, and the relation, once attained, becomes fixed. (9) In Hydroides norvegica at least, the opercula show a tendency to right-handed growth from the beginning of their development, but this condition of asymmetry is very unstable and is easily reversible by an external influence even in the adult state, i.e. there is no critical stage at which it is irreversibly determined.

additional specimens of A. gunneri floridus were found in the same location in June and July; one of these was parasitized. Only two species of digenetic trematodes which use annelids as first intermediate host have been reported: Cercaria loossi Stunkard, 1929, from the coelom of the serpulid polychaete Eupomatus dianthus (Verrill) (also known as Hydroides hexagonus (Bosc) and H. dianthus (Verrill)), in the Woods Hole region, Massachusetts (Linton, 1915a; Stunkard, 1929; Martin, 1944a; Rankin, 1946); and Cercaria hartmanae Martin, 1952, from the coelom of the terebellid polychaete Lanicides vayssierei (Gravier), dredged from near Ross Island, Antarctica (Martin, 1952). The present cercaria is herein described as Cercaria amphicteis n. sp. Both living and preserved rediae and cercariae were studied. Neutral red was used to