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Protrusions of bounding membranes of neurosecretory granules, comparable to those demonstrated by Castel (1977) in the mammalian neurohypophysis, were observed under various experimental conditions in the corpora cardiaca of the insects Leucophaea maderae and Periplaneta americana. Electrical stimulation in vitro of the nervus corporis cardiaci I, which elicited a marked rise in the amount of neurohormone discharged, as determined by bioassay, also yielded a significantly larger number of membrane protrusions than were observed in unstimulated controls. However, no comparable response was obtained in glands subjected to stimulation of hormone release by exposure to serotonin or high potassium concentrations. On the other hand, membrane protrusions were numerous under certain conditions not expected to stimulate neurohormone release, i.e., in tissue exposed to a zinc iodide mixture without prior fixation. The present results support the conclusion drawn by Castel that these configurations appear to be related to the process by which neurosecretory material is discharged. Too transient to be much in evidence under physiological conditions, they become more prominent not only after appropriate acceleration of the rate of release, but also when such membrane arrangements are “frozen” by procedures that interfere with the regular milieu.

Ultrastructural changes were examined in corpora cardiaca ofPeriplaneta americana in which acute electrical stimulationin vitro had brought about hormone release.

Growing oocytes of Protopterus, like those of some amphibians and teleosts, show an impressive development of the nucleolar apparatus. Numerous nucleolus-like bodies establish close spatial relationships with the nuclear envelope by extending pedicels and streams of finely dispersed material towards the inner membrane.

In der Paraphyse der Amphibien werden Erythrocyten abgebaut. Sie werden von Reticulumzellen aufgenommen, die mit dem abgebauten Material der roten Blutkörperchen als Meningocyten (Cushing) aus dem Paraphysenbereich auf die Oberfläche der inneren Duralamelle auswandern. Auch hier sind sie an der Phagocytose abbaureifer Erythrocyten beteiligt. Die Meningocyten finden sich nicht im strömenden Blut und nicht in anderen Körperorganen. Es handelt sich also um spezifische freie Zellen der Paraphyse und der Meningen der Amphibien.

1.Die bei vielen Wirbeltieren beobachteten Vorgänge der Neurosekretion im Hypothalamus werden bei einem Vertreter der Selachier, Scyllium stellare, beschrieben.2.Wie bei anderen Wirbeltieren wird auch bei Scyllium das von den Zellen des Nucleus praeopticus produzierte Neurosekret entlang den Fasern des Tractus praeoptico-hypophyseus zur Hypophyse abtransportiert.3.Die Endigungen der sekretführenden Nervenfasern sind nicht wie bei anderen Wirbeltieren auf eine gesonderte Pars nervosa beschränkt. Die Pars nervosa von Scyllium ist diffus und mit der Pars intermedia innig vermischt.

The ultrastructural characterization of the prothoracic glands derives interest from the fact that they are the only known source of a steroid hormone (ecdysone) among invertebrates. The present material includes nymphal glands of two blattarian species studied at graded intervals over a period of several intermolt cycles.

A specialized type of trophospongium has been described in large nerve cells of the cerebral ganglion of the planktonic crustacean Leptodora kindtii. It consists of three parts (Fig. 6). The first is, as a rule, long; it is composed of an infolding of the plasma membrane of the neuron, an intercellular space and a slender process of a glial cell. The second segment from the end of the glial process to the beginning of the X-body is always short; it is characterized by the presence of a desmosome-like junction. The third part consists of a labyrinth of cisternal spaces lined by membranes which are continuous with the infoldings of the surface membrane of the nerve cell.

The structural differences between active and inactive corpora allata, visible under the light microscope, become more pronounced under the electron microscope. Aside from differences in cellular and nuclear diameters, and nuclearcytoplasmic ratios, there are qualitative characteristics in ultrastructural organization.

Groups of large cells in the cerebral ganglion of Leptodora kindtii join in intricate patterns to enclose lacunar spaces. The cell surfaces bordering on these lacunae are covered by long, densely packed microvilli that all but fill the spaces. Near their “brush borders” the cells are joined by adhesion plates; for the rest they are separated from each other by glial septa. The possible significance of these structures is discussed.

The prothoracic glands, source of the molting hormone ecdysone, regress within a few days after the final molt, a process which was analyzed with electron microscopic methods in the cockroaches Leucophaea and Blaberus. This strictly timed event is accompanied by drastic alterations in cellular fine structure. Early signs of breakdown appear in groups of nuclei whose substance becomes segregated into patches of contrasting electron density characteristic of pyknosis.

Ultrastructural specializations characteristic of sites of release of neurosecretory material from axons were examined in several species of blattarian insects. Discharge of such material may take place within or outside of neurohemal organs and is not restricted to fiber terminals. Structurally distinctive areas serving this function occur intermittently and may be more or less transient. Many of these specialized zones face the extracellular stroma that forms sheaths and partitions of neurohemal organs (corpora cardiaca, perisympathetic organs), others contact various cellular elements (nerve fibers with or without neurosecretory granules, glial cells, non-neural endocrine cells).

Ultrastructural evidence is presented for the manufacture, storage, and release of a distinctive cellular product in the corpus allatum of the insect Leucophaea. This product (C body material) originates in the Golgi zone and acquires a characteristic, regularly structured appearance of exceptionally high electron density.

The wide range of functional activities of circulating and sessile insect hemocytes expresses itself in highly specialized cytological terms. Electron microscopic studies carried out in five species of normal and experimentally manipulated cockroaches, in conjunction with light microscopic information, reveal a broad spectrum of structural organization and an apparent capacity for cellular modulation. In addition to conventional organelles, these hemocytes contain a class of unusual cytoplasmic inclusion bodies which seem to undergo striking transformations in response to specific functional demands. A variety of transitional forms attests to the existence of close links between tubule containing (type 1), electron dense (type 2), and large globular (type 3) inclusion bodies, and reveals the derivation of yet another special (lamellated, fusiform) inclusion from type 2 bodies. Confluence of the type 3 configurations into still larger lacunae may precede the release of their contents into the hemolymph, a process whose major effect seems to be the initiation of the clotting process.

The granules of neurosecretory cells in the supraesophageal ganglion of the earthworm, Lumbricus terrestris L., are formed by the Golgi apparatus. The process of neurosecretion is discussed in relation to this observation.

The corpora cardiaca of Leucophaea maderae contain two classes of intrinsic elements, parenchymal and interstitial cells. The parenchymal cells produce a secretory material first visible in the Golgi zones of the perikarya in the form of distinct electron-opaque granules. These undergo changes (gradual loss of electron-density, emergence of internal structure) as they accumulate in cellular processes.