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Studies of the blood cells and tunic of the ascidian, Halocynthia Aurantium (Pallas) Smith, Michael Joseph

Abstract

The morphology and histochemistry of the blood cells and tunic of the ascidian Halocynthia aurantium were studied. The nature of the tunic was investigated by both chemical and biochemical means. Quantitative studies of the blood of Halocynthia display ten blood cell types, four of which are concentrated in tunic in higher concentrations than in blood. Of these four, two, including an iron bearing cell, display discrete stable aggregation areas in the body of the tunic, and a third is a phagocyte. Histochemical examination of the tunic and blood cells reveals that the tunic fibers and epidermis stain for acid mucopolysaccharide and protein. The spinous processes on the surface of the tunic do not stain like the epidermis or fibers, but do display some similarity to the blood cell type which aggregates in their proximity. There is a coincidence of absorption spectra of methanol extracts of blood cells and tunic, but no particular blood cell has been indicated as the pigment cell. The blood cells, in the tunic, do not display staining properties which would indicate that they are contributing to the carbohydrate component. Morphological characteristics and histochemical properties of epidermis indicate that it is the major tunic secreting tissue. The histogenetic relationship of various blood cells is discussed on the basis of analogous histochemistry and quantitative hematology. The function of particular blood cell types in the tunic is suggested by the discrete positional relationships of cells and the morphology of the tunic. The chemical composition of tunic is approximately 50% protein and 50% carbohydrate. Amino acid analysis of tunic before and after proteolytic enzyme treatment shows that the protein does not have the characteristics of common connective tissue proteins such as collagen, elastin, or others, and that the protein-polysaccharide link probably involves glucosamine and serine. Five per cent of the dry weight of tunic is hexosamine with both galactosamine and glucosamine present in a ratio of 1 to 4. The carbohydrate component of the tunic releases 75% of its weight as glucose upon acid hydrolysis. This carbohydrate consistently displays a negative P.A.S. reaction and is resistant to several cellulose dispersing reagents. The elemental composition of the carbohydrate reveals a hydrogen content which is too low and an oxygen content which is too high to indicate cellulose. Tunic, pronase treated tunic, and tunic carbohydrate were submitted to cellulase, chitinase, and hyaluronidase digestion. None of these materials are subject to degradation by chitinase or hyaluronidase. Tunic is refractory to cellulase. Pronase treated tunic will release 20% of its weight as glucose upon incubation with cellulase. Tunic carbohydrate component will release 55% of its weight as glucose upon cellulase treatment, although chemical properties indicate that it may be more complex than cellulose.

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