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The thymic rudiment in mice homozygous for the recessive mutation nude (nu) has been compared to the normal at two stages: the 14-to 15-day foetus and the 1-to 2-day-old young. In the former, the normal thymus already comprises two adjacent lobes but in the nude it is represented by a pair of thin strands of tissue, each with a narrow central lumen. In further development these strands become thicker and vesiculated. They progress no further and are found in the 1-to 2-day young as small vestiges that are never populated with lymphoid cells. The thyroid, parathyroids and mandible of homozygous nude mice are normal, indicating that the complex of structures derived from the third branchial arch is not affected as a whole.

1. On removal of one dorsal mesothoracic disc from third-instar larvae ofDrosophila melanogaster (wild stock), regulation took place in one fourth of the cases, by the activity of the corresponding disc of the intact side. 2. In larvae of abithorax stock, regulation took place in the majority of cases, but it was due to the activity of thebx dorsal metathoracic disc of the operated side. 3. The sternopleura is present after extirpation of the wing disc but absent after extirpation of the ventral mesothoracic disc. 4. The findings under 1 and 2 are discussed in connection with previous work on regulation in larval discs.

Experimental evidence is produced to show that during metamorphosis in Drosophila melanogaster: The growth-of the lateral oviducts depends on an influence of the ovaries. The growth of the ovaries does not depend on a reciprocal influence. The growth of the vasa deferentia is independent of any influence from the testis.

SUMMARYComparison, by electrophoretic methods, of eel samples from Iceland, Scotland and Germany confirmed previous reports of uniformity in haemoglobin types. When liver esterases were examined, significant differences in the frequencies of phenotypes in the ‘fast’ zone of the electropherogram were found between samples from Germany and samples from Iceland and Scotland. The frequencies of transferrin phenotypes in Icelandic and Scottish eels differed significantly from those of French and American eels.It follows that regional differences in gene frequencies probably exist within the speciesAnguilla anguilla. The implications for the ‘atlantic eel problem’ are briefly discussed.

The ‘typical’ serum esterase zymogram, obtained by starch-gel electrophoresis, of adult mouse serum comprises 19 fractions, but undergoes changes related to developmental stage. The main adult fractions are already present in the 18-day foetus. Whilst most are weaker than in the adult, the reverse is true for fractions 16–19. There are also six ‘foetal esterases’ which gradually decrease and disappear after birth, at different rates. The foetus and the young animal, up to 2 weeks, have also alkaline phosphatase (1 or 2 fractions), whilst no such enzyme was detectable in the adult’s serum. Pregnancy is associated with increases in three and decreases in two adult fractions and, more characteristically, with the appearance of a strong specific pregnancy esterase. An esterase zone (6) which is always stronger in the male could be subdivided into three fractions in males and two in females. The exclusively male fraction coincides with a band of acid phosphatase activity.

The inheritance of three lymph protein fractions separable by starch-plate electrophoresis has been studied. Each fraction is under the control of a separate gene, the dominant allele determining its presence and the recessive its absence.The gene for the fastest fraction is sex-linked, whilst those for the other two are autosomal and linked.

Ovaries of an inbred line, L25, selected for large body size, were transplanted (at the third-instar larval stage) into hosts of a line, ES4, selected for small body size. The operated individuals were mated to males of the donor small line and produced two types of offspring: hybrids of the two lines and homozygotes of the ‘large’ line. Thorax and wing length measurements of the latter offspring group and of control ‘large’ line offspring were taken and compared. Statistical analysis of the data showed a significant. reduction in the thorax and wing size of female and in the wing size of male offspring from transplanted ovaries. This reduction, however, amounted to only 3 % of the size difference of the two lines.

Images Figs. 4-6 Figs. 1-3

“Nude” (thymusless) mice immunized with sheep red cells gave rise to indirect PFC in numbers (per million spleen cells) that were comparable to those of normal animals for days 2 - 4, but declined sharply thereafter. Hemolysin and hemagglutinin titers follow essentially the pattern of the direct PFC response. About two-thirds of nude animals also formed some indirect hemolytic plaques which are interpreted as due to 7 S (IgG) globulins rather than to low efficiency 19 S (IgM) globulins. In the secondary response, nude mice failed to exceed their primary performance in any of the four parameters measured: direct PFC, indirect PFC, hemolysin titers and hemagglutinin titers, thus demonstrating the thymus dependence of immunological memory. The initial spurt of immunological reactions by nude animals, followed by premature decline suggest a failure of proliferation or recruitment of immunologically responding cell population in the absence of a thymus.

Iron-59 (as a ferric chloride solution or as a component of haemoglobin) was introduced into the lumen of the gut of Fasciola hepatica. It was detected by autoradiography in high concentrations in the intestinal epithelium, the cuticular epithelium, the myoblasts and the cells forming the walls of the excretory tubules. Carbon-14, introduced as l-phenylalanine-C-14, was concentrated in the same tissues, with the exception of the intestinal epithelium. These findings are discussed in relation to the function of the respective tissues.

Electrophoretic studies on starch gel demonstrated the existence in the European eel of four haemoglobins, not two as believed from agar gel studies. The two minor fractions have been shown to be neither polymers nor methaemoglobin derivatives of the two principal fractions.The esterase zymograms of eel sera exhibit up to eight fractions. The individual differences observed suggest genetic polymorphism and the same applies to the esterase pattern of various tissues.This approach is of value for the collection of phenotypic frequency data with a view to solving the Atlantic eel problem.

1. The existence of a difference in thorax size between the male offspring of reciprocal crosses of large and small selectedDrosophila strains was confirmed. A similar and larger difference was observed in wing length. These differences can be enlarged to a varying extent by lowering the temperature dining the larval or pupal or both stages. 2. The percentage of length increase is approximately the same for the thorax and the wing when temperature is kept low during the larval stage only. But the wing increase becomes six times larger than the thorax increase if the temperature is lowered during the pupal stage only. This is probably correlated to changes, in opposite directions, of the metabolic patterns in the primordia of the two organs. 3. The wing-length to thorax-length index increases with the lowering of temperature. This increase has been compared to the differences in this index appearing between various species of Drosophilidae.

Chick blastoderms of the definite primitive streak stage were cultured in vitro for about 24 hours with radioactive DL-methionine-S35 added to the medium. It was shown by autoradiography that the neural tube and especially its roof and also adjacent areas of the ectoderm (neural crest) take up more activity than other structures. Mesodermal structures such as the notochord, somites, and myoepicardium also reach a high level of uptake, presumably correlated with their differentiation. Tissues of the host, the induced axis, and self-differentiating (non-labelled) grafts take up activity from the culture medium at the same rate. If a labelled organizer is grafted on to a host blastoderm, the induced neural tube takes up a substantial amount of labelled molecules but the host does not. Experiments involving dilution with unlabelled methionine or grafting of labelled peripheral organizer tissue, produced evidence for the view that the activity is carried to the induced tissues by diffusion or exchange of free aminoacid molecules; transfer of macromolecules does not occur on a scale detectable by the methods used but it cannot be excluded that it might occur on a smaller scale. In cases of induction caused by organizer graft the notochord, mesenchyme, and, occasionally, tissues lining the foregut associated with the induced axis are contributed by the graft.

An mannlichen und weiblichen Drosophilalarven im dritten Larvenstadium lassen sich die Gonaden durch Hindurchleiten eines hochfrequenten Wechselstroms (Frequenz 20 000 Hz, Stromstarke empirisch) ohne Schadigung anderer Organein situ zerstoren. Die Methode ist bei Mannchen erfolgreicher als bei Weibchen. Die Versuchsanordnung und die Herstellung einer geeigneten Mikroelektrode werden beschrieben.

Summary Athymic (homozygous nude) mice of a non-inbred stock had relatively little antiviral activity in their serum compared with normal control mice at 4, 6 and 6.5 h after the intraperitoneal injection of Newcastle disease virus. The antiviral activity in the serum had the characteristics of interferon. At 10 h after injection and thereafter, the serum titres were comparable in nude and normal control mice. Exceptional nude mice with thymus-like tissue sometimes produced interferon more or less normally. Transfer of spleen cells from normal donor mice, but not from nude donors, led to increased serum interferon levels in nude recipient mice at 4 h after virus injection.

The anterior pituitary of athymic homozygous "nude" (nu nu) mice shows signs of reduced activity of the acidophilic cells, nuclear volumes of which lag significantly behind normal values. Also there is a significant deficiency in the number of basophilic cells. A similar deficiency is found in the numbers of Purkinje cells of the cerebellum, which in addition also show a reduction in size, as part of an overall reduction of cerebellum size.

1. 1. A study was made of the weight changes of adult liver flukes (Fasciola hepatica L.) held in Hedon-Fleig media of various concentrations, and in Hedon-Fleig to which glycerol, glucose, galactose, sorbitol, sucrose or maltose was added. 2. 2. Flukes survived for at least 6 hr in Hedon-Fleig media of freezing-point depression from 0.40–0.81°C. They did not appear to regulate their water content during this time. 3. 3. Of the carbohydrates, sucrose and maltose exerted the greatest osmotic effect (i.e. loss in weight) and glycerol the least; glucose, galactose and sorbitol all had an intermediate effect. A possible intepretation of these findings in terms of the relative permeability of the fluke to the compounds is discussed.

In this second article on Greek science, E M Pantelouris, assesses the effort put into non-university research.

MICE homozygous for the mutation, nude (nu) have been reported to have no thymus1, although they retain a prelymphoid thymic rudiment2. Here, I report the occurrence of individuals that are by external signs (including hairlessness) a nude mutation but possess an apparently normal thymus.

THE controversy about the identity of the European eel was started by Tucker in 19591. Contrary to the theory of Schmidt2, which assumed that both European and American eels return for spawning to the Sargasso Sea, Tucker argued that it is unlikely that the eels from the European waters manage to return, and that the eels which spawn in the Sargasso Sea are therefore all American. If this were true, the European eel should originate from the same gene pool as the American eel, and have identical gene frequencies, unless differential mortality changes these frequencies.

ONE of the most fundamental problems, both for genetics and embryology, is that of whether the genes in the nuclei of differentiated tissues retain their full range of capacities, or whether some irreversible alteration affects them. The most direct method of investigating this is to develop techniques which permit the transplantation of nuclei from differentiated cells of one kind into enucleated cells of different developmental potentialities. Briggs and King1 have reported some attempts in this direction, in which nuclei from blastulae or early gastrulae of frogs were injected into uncleaved but fertilized frogs' eggs from which the zygote nucleus had been removed. Nuclei from blastulae permitted the full differentiation of a normal embryo in a fairly high proportion of cases, those from early gastrulae in a smaller proportion, whereas those from determined (but not yet differentiated) tissues gave little success, though it remained uncertain whether this was due to technical difficulties or to an incapacity of the genes.

Thymus and Self: Immunobiology of the Mouse Mutant Nude †. By Jorgen Rygaard. Pp. 193. (Wiley-Interscience: London and New York, March 1975.) £6.50.

Gruppen von 2–4 somatischen Kernen haploiderTriturus-Embryonen wurden in diploide, ungefurchte Eier injiziert, 11 haplo-diploide Mosaik-Larven entwickelten sich bis zum fruhen Neurula-Stadium. Nachkommen von Kernen aus dem neuralen Ektoderm oder Chorda-Mesoderm von Spendern im Neurula-Stadium fanden sich in allen drei Keimblattern der Wirtslarve.