. A text-book of invertebrate morphology. Invertebrates. 384 INYERTBERATE MORPHOLOGT. The second nephridium (Fig. 172, B) develops in connec- tion with the second maxillary segment, and opens usually upon the appendage of that segment. It is especially devel- oped in the Entomostraca, in which it may lie in the folds of the body-wall which form the shell, and hence is usually known as the shell-gland. It occurs also in the larval stages of many Malacostraca, and may possibly persist in a degen- erated condition in the adults of some forms. In structure it. sa Fig. 173.—A, Diageam of Nephbiditi
. A text-book of invertebrate morphology. Invertebrates. 384 INYERTBERATE MORPHOLOGT. The second nephridium (Fig. 172, B) develops in connec- tion with the second maxillary segment, and opens usually upon the appendage of that segment. It is especially devel- oped in the Entomostraca, in which it may lie in the folds of the body-wall which form the shell, and hence is usually known as the shell-gland. It occurs also in the larval stages of many Malacostraca, and may possibly persist in a degen- erated condition in the adults of some forms. In structure it. sa Fig. 173.—A, Diageam of Nephbiditim (Gbeen-gland) of Astacus (after Marchal); B, Shell-gland of Wulimnadia. s = terminal sac. sa = saccule. resembles closely the antennary gland, but does not present the complexity frequently found in that gland. The majority of the Crustacea are bisexual, hermaphro- ditism occurring only in forms which have a parasitic habit and in some which are sessile in adult life (Cirrhipedia). The ovaries or testes (Figs. 173, A and B) are paired organs lying alongside of the intestine or slightly dorsal to that organ, transverse connecting bars in some cases passing from the organ of one side to that of the other. Each organ may be regarded as a tube, sometimes simple, sometimes branched, and lined on its interior by an epithelium which gives rise to the germ-cells. Special germ-producing regions are fre- quently developed, as, for instance, at the extremities of the tubes or along one side (Isopoda), the cells in other regions ceasing to give rise to ova or spermatozoa. The reproductive elements pass to the exterior by special ducts, oviducts (od). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original McMurrich, J. Playfair (James Playfair), 1859-1939. New York, H. Holt and Company
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