Publisher Summary This chapter discusses basic concepts and advances of invertebrate immunity. In mammals and other higher vertebrates, a plethora of information exists on the origin, development, structure, and functions of the cells and tissues of the immune system. The cells of the invertebrate immune system can be subdivided into two main groups—namely, the freely circulating blood cells/coelomocytes and a variety of fixed cells. These latter cells may be either scattered throughout the tissues or localized together in hemopoietidphagocytic organs. In addition to these cell-mediated defenses, there are a number of chemical and mechanical barriers to parasite invasion. The chapter also explains the structure and classification of blood cells/coelomocytes. It provides a functional approach for blood cell classification and the cells are arranged into five main groups—namely, progenitor cells, phagocytic cells, hemostatic cells, nutritive cells, and pigmented cells.

Invertebrate Immunity: Basic Concepts and Recent Advances

municable disease control to the newer responsibilities of the hazards of ionizing radiation and medical defense against atomic attack. The individual topics are adequately developed with emphasis, in the majority, on brevity of presentation rather than complete and exhaustive detail. References are listed after each chapter for the reader desiring more definitive information. \"Epidemiologic Methods and Inferences\" by Dr. Dienfeld and \"Official and Voluntary Health Agencies\" by Dr. Hilleboe are two chapters which offer especially well-organized, succinct, and effective discussions of their respective subjects. The editors state in their preface that they are presenting \". . a new way to look at preventive medicine for the medical students, general practitioners, specialists, and professional workers in official and voluntary health agencies.\" In the opinion of the reviewer, the authors have achieved their purpose by editing a book which is more an introductory text than a reference tome.

Histochemistry, Theoretical and Applied.

The cellular processes involved in metal metabolism in molluscs are reviewed, with emphasis on the contribution of microscopy (AMG, ARG, EPMA, and SIMS) to both basic research of metal cell biology and applied environmental research. In molluscs, metal uptake may occur by facilitated diffusion, active transport, or endocytosis, and can be enhanced by MT synthesis or formation of mineralized granules. In aquatic molluscs, gills constitute a key interface for dissolved metal uptake, where metals are bound to MT, incorporated into lysosomes, and released basally towards the blood plasma and circulating hemocytes. However, particulate metal uptake is mainly achieved via the digestive tract by endocytosis; further metals are transferred first to lysosomes and then to residual bodies, especially in the digestive cells of the digestive gland. Additionally, metals can be accumulated selectively in specific cell types. As ligands pools differ from cell to cell, different metals may be retained in different cell types. Class "a" metals are localized in cells with granules composed of carbonate, oxalate, phosphate, and sulfate (oxygen donors), whereas "b" metals are associated with those cell types rich in sulfur and nitrogen ligands (sulfur donors). In molluscs, oxygen donors occur in connective tissue calcium cells and basophilic cells, whereas sulfur donors are present in digestive cells, podocytes, nephrocytes, and rhogocytes. Hemocytes, which constitute the most relevant system for metal transport between tissues, move around the body and may penetrate tissues and remove metals from the inner medium to be accumulated in lysosomes as nondigested products. Rhogocytes also participate in metal mobilization, accumulation, and release. The assessment of metal levels in target cells of sentinel molluscs by microscopic techniques provides an early-warning measure, with promising applications as an exposure biomarker for environmental monitoring programs.

Cellular and subcellular distribution of metals in molluscs.

The morphology and the ultrastructure of the blood and connective tissue cells of Lymnaea stagnalis were studied. Special attention was paid to the role of these cells in the cellular defense mechanism (phagocytosis). This problem was investigated in injection experiments with enzyme histochemistry and electron microscopy.

Structure and function of blood and connective tissue cells of the fresh water pulmonate Lymnaea stagnalis studied by electron microscopy and enzyme histochemistry.

Neuroendocrine control mechanisms are observed in all animals that possess a nervous system. Recent analyses of neuroendocrine functions in invertebrate model systems reveal a great degree of similarity between phyla as far apart as nematodes, arthropods, and chordates. Developmental studies that emphasize the comparison between different animal groups will help to shed light on questions regarding the evolutionary origin and possible homologies between neuroendocrine systems. This review intends to provide a brief overview of invertebrate neuroendocrine systems and to discuss aspects of their development that appear to be conserved between insects and vertebrates.

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The neuroendocrine system of invertebrates: a developmental and evolutionary perspective

The various stages of spermatogenesis and the Sertoli cells of Biomphalaria glabrata were studied with histochemical and electron microscope techniques. During spermatogenesis a manchette of microtubules is formed around the nucleus and the mid-piece of the spermatids. This manchette becomes helically coiled and probably plays an important role in the spiralisation of the nucleus and of the mitochondrial sheath. During spermatogenesis so-called chromatoid bodies (CB) occur, which consist of arginine-rich proteins. These CB disintegrate during the early spermatid stage. The results suggest that the CB are either involved in histone transition or in the formation of microtubules. The remaining cytoplasm of the spermatids is phagocytised by the Sertoli cells. Apparently this process of phagocytosis is an important part of the mechanism of spermiation. Morphological measurements of the Sertoli cells showed that the relative volume of most organelles decrease during spermatogenesis, indicating a general decrease in cell activity. Possible functions of the Sertoli cells, such as transportation and nutrition of spermatogenic cells and hormone production, are discussed. It is concluded on the basis of the histochemical and ultrastructural observations that the Sertoli cells are involved in the nutrition of spermatogenic cells. It seems unlikely that they are hormone producing cells.

Spermatogenesis and the role of Sertoli cells in the freshwater snail Biomphalaria glabrata

In the freshwater snail Biomphalaria glabrata the formation and composition of yolk granules and the role of the follicle cells were studied by histochemical and electron microscopical techniques. The rough endoplasmic reticulum and the Golgi apparatus appeared to be involved in yolk formation, which is a continuous process throughout oogenesis. From the very beginning of yolk formation two main types of yolk granules were distinguished morphologically. However, with histochemical and enzyme cytochemical methods no differences were observed between these types. The granules acquire lysosomal enzymes after oviposition, indicating that their main function is probably digestion of perivitelline fluid, which contains nutrients for the developing embryo. Yolk formation and the activity of the follicle cells were studied in successive stages of oogenesis by quantitative electron microscopy. The data strongly suggest that the follicle cells are involved in the formation of the follicular cavity and hence in the ovulation process.

A light and electron microscope study on oogenesis in the freshwater pulmonate snail Biomphalaria glabrata.

A neuropeptide (Calfluxin) is involved in the influx of calcium into mitochondria of the albumen gland of the freshwater snail Lymnaea stagnalis

The ultrastructure of the slit diaphragms between the pedicels of the podocytes of the prosobranch Viviparus viviparus and between the cytoplasmic tongues of the haemocyanin producing pore cells of the pulmonate Lymnaea stagnalis was investigated. In both cell types 2 diaphragms are present in the slits. They form a 3-dimensional sieve structure with holes of respectively 90 × 110 A (podocyte) and 200 × 220 A (pore cell). Injection experiments showed that the size of the holes of the pore cell sieve matches that of particles which can be ingested by this cell type. The substructure of the sieves of the molluscs is compared to that of the 2-dimensional sieve of the podocytes of the mouse and the rat.

Sieve structure of slit diaphragms of podocytes and pore cells of gastropod molluscs.

The ultrastructure of the organs involved in urine production in the pond snailLymnaea stagnalis is described. The atrial wall, which has been assumed to act as an ultrafilter, shows little ultrastructural correspondence with other ultrafilters, such as the mammalian glomerulus. Thus, ultrafiltration probably can take place in systems lacking the typical podocytes. The atrium of the stylommatophoreHelix pomatia appeared to differ only in quantitative aspects — it is thicker — from that of the basommatophoresL. stagnalis andBiomphalaria glabrata. The reno-pericardial duct consists of ciliated columnar cells, which contain considerable amounts of glycogen. The cells of the kidney sac are characterized by the presence of large (5–20 μ) excretion granules, which are constricted off together with part of the cytoplasm. In degenerating nephrocytes great numbers of lipid granules, probably arising from mitochondria, were found. Deposits of glycogen are present in the nephrocytes as well as in the cells of the ureter, suggesting the kidney to be a glycogen storing organ. The presence of glycogen is accompanied by that of an elaborate agranular endoplasmic reticulum. Although relative differences in the general ultrastructural pattern of the kidney sac and the ureter were found, some aspects of both epithelia—viz. the presence of numerous large mitochondria, a zone of microvilli at the free cell surface, and prominent infoldings of the basal and lateral cell membranes — suggest them to be involved in the reabsorption of solutes and in the transportation of ions and water.

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H. H. Boer

Papers

Spermatogenesis and the role of Sertoli cells in the freshwater snail Biomphalaria glabrata

A light and electron microscope study on oogenesis in the freshwater pulmonate snail Biomphalaria glabrata.

A neuropeptide (Calfluxin) is involved in the influx of calcium into mitochondria of the albumen gland of the freshwater snail Lymnaea stagnalis

Sieve structure of slit diaphragms of podocytes and pore cells of gastropod molluscs.

Ultrastructure of the reno-pericardial system in the pond snail Lymnaea stagnalis (L.).