§ 290, THE CRUSTACEA. 349 



probably, some relation between this remarkable mode of generation and the 

 fact that some females lay two kinds of eggs, one of which is developed 

 spontaneously, that is, without the influence of sperm, while the other re- 

 quires to be fecundated/-^ 



The structure and disposition of the genital organs is so different in the 

 various divisions of Crustacea, that it is diificult to make any general state- 

 ment about them. Usually, there is a complete duplication of these organs, 

 internal and external, with both sexes. With the females, there is nearly 

 always, right and left, a longer or shorter, rarely-branched, ovarian tube. 

 This is succeeded by a narrow oviduct, usually long, and often flexuous. This 

 last continues into a large vagina, which opens at very different points on 

 the ventral surface, sometimes quite in front, sometimes near the middle, 

 or at the posterior extremity. It is rare that this vagina has a Receptacu- 

 lum seminis ; but, more commonly, the females have special glandular 

 canals annexed to the genital orifice. The product of these last is a viscous 

 mucus, which hardens in water, and serves to envelop the eggs, and to glue 

 them together. The eggs, thus bound together in chaplets or clusters, 

 remain glued to the parts neighboring the genital orifice, or to the post- 

 abdominal feet, and are borne about by the females, until the embryos 

 are fully developed. With other females, where these organs are wanting, 

 they are replaced by a special pouch [Marstipium) situated, usually, at the 

 inferior surface of the thorax. In this pouch the eggs are deposited and 

 remain until their embryos are completely developed. 



With the males, the internal genital organs are dispof'^d in a similar 

 manner, and often have the same form as those of the females. A 

 careful examination is, therefore, necessary, to perceive their distinctive 

 character. Moreover, they open, also, at the most varied points of the 

 body. In many species, there are, near the genital orifices, copulatory 

 organs in the form of stylets, or canaliculi, which serve to transfer the 

 sperm into the female organs. With others, the antennae, or some of the 

 feet, are provided with a kind of hook, or pincers, with which they seize 

 and retain the females during copulation. Sometimes the internal organs 

 of the left communicate, by anastomoses, with those of the right side, or, in 

 the place of two lateral genital openings, there is only one, situated on the 

 median line. With many species, the genital organs, internal and external, 

 are simple, and placed in the axis of the body ; but it is rarely observed, 

 that the oviducts and deferent canals are single where the ovaries or the 

 testicles are double, or that there are two genital openings for single in- 

 ternal organs. 



The Eggs of the Crustacea are usually of either a lively green, yellow, 

 or violet color. They are always spherical, and composed of a dense 

 chorion, containing a vitellus, which surrounds a germinative vesicle, with 

 one or more nuclei. The vitellus is composed of numerous oil-globules, 

 which are held together by a clear, albuminous liquid, and give the egg its 

 peculiar color.'^> 



The sperm is white and sometimes opalescent. The spermatic particles 

 are of very varied and remarkable forms. Nearly always, they are 



2 This phenomenon is undoubtedly analogous to mal. Crust, general., 1844, and his Bcmerkungen In 

 that of the alternation of generation, which is so Froriep^s neue Notiz. XXIV. 1842, p. 181 ; Erdl, 

 general with the other lower animals. Entwickelung d. Ilummereies, p. 13 ; and especially 



3 For the eggs of Crustacea, see Rathki, De Anl- Wagner, Prodromus, &c., p. 8, Tab. I. fig. 13-17. 



30 



