THE MOLTING CYCLE OF THE SPINY LOBSTER, PANULIRUS ARGUS LATREILLE. II. PRE-ECDYSIAL HISTOLOGICAL AND HISTOCHEMICAL CHANGES IN THE HEPATOPANCREAS AND INTEGUMENTAL TISSUES

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Abstract
In Panulirus argus. the integumental tissues are composed of columnar epidermal cells and a sub-epidermal connective tissue of a loose spongy type. Large oval reserve cells constitute by far the most predominant type of cells in the sub-epidermal tissue. These cells store abundant amounts of carbohydrate, lipid and Ca at various stages throughout the molting cycle; they are also found in the hepatopancreas. Within the tubular epithelium of the hepatopancreas are two major types of cells, secretory and absorptive. The former are swollen cells containing very large vacuoles at their distal ends. Secretion is of the apocrine type, leaving only the basal region and nucleus of the cell intact. Reconstitution of secretory cells probably occurs by regeneration from the remaining basal ends. The absorptive cells are tall and cylindrical with a basal or central nucleus. During the intermolt period (late Stage C), a period of active feeding, there is little glycogen, phosphatase, and Ca evident in either the hepatopancreas or the integumental tissues. Lipids, however, are abundant in the epithelial tissues of the hepatopancreas. During the pre-ecdysial period (late Stage D) large numbers of reserve cells of the integumental tissues become greatly swollen, and bind or store large amounts of polysaccharide material. Glycogen is abundant in the epithelial tissues of the hepatopancreas and simultaneously accumulates in the epidermal cells of the inner integument as it is being formed. Available evidence would suggest strongly that glycogen is a necessary precursor for chitin formation. Furthermore, glycogen is perhaps intimately involved in the deposition of calcospherites which accumulate in the hepatopancreas during this time. Integumental tissue phosphatase appears in the distal ends of the epidermal cells bordering the integument and in reserve cells of the connective tissue. It is suggested that phosphatase, in these strategic sites of active transfer, probably participates in producing molecules which are able to enter or leave the cells more readily, and in those reactions involving hydrolysis and dephosphorylation of glucose phosphate to glucose, a possible starting point for chitin formation. It is not participating in calcification of the branchial integument at this time, because calcification does not begin until the second day following molt. In the hepatopancreas, on the other hand, alkaline phosphatase is heavily concentrated at the striated borders of the absorbing cells and around Ca deposition sites (calcospherites). Here the enzyme appears to be involved in important transfer and dephosphorylation reactions which occur at the surface of the absorbing cells and also to be intimately concerned with the deposition of calcium phosphate at the periphery of these same cells. Evidence available suggests that lipids, abundant in the hepatopancreas at this time, function as a major source of energy. Furthermore, the accumulation of fatty acids, glycerides, and other intermediates of oxidative as well as glycolytic metabolism during late Stage D and Stage A may contribute to the rise in osmotic pressure preceding molt, facilitating water uptake. Further evidence suggests that some of the fatty acids, cholesterol and unsaponifiable fatty acids conveyed to the integumental tissues preceding molt are used in the formation of the epicuticle.

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