FEMALE GENEEATITE OEOANS. 



413 



Fig. 208. 



brood to a single impregnation by the male, and that the male can only 

 impregnate the female immediately after the shedding of the exuviae. 

 " For days previously the male may be seen running about and hiding 

 himself under stones, holding the female by one or more of his legs, the 

 carapace being pressed against the sternum of the male. In this relative 

 position they continue until the female throws off her calcareous clothing, 

 when connexion immediately follows, and continues perhaps for a day 

 or two." 



(1060.) The female generative organs of Crustacea very accurately 

 resemble those of the male ; and in 

 the unimpregnated condition it is 

 not always easy, from a superficial 

 survey of the internal viscera, to 

 determine the sex. In Astacus 

 fluviatilis, the ovaria (fig. 208, a) 

 occupy a position analogous to that 

 of the male testis, and a simple 

 canal derived from each side (6, c) 

 conducts the eggs to the external 

 apertures found upon the first joint 

 of the third pair of legs. 



(1061.) In Crabs, an important 

 addition is made to the female 

 generative system: prior to the 

 termination of each oviduct it is 

 found to communicate with a wide 

 sacculus, the function of which is 

 apparently analogous to that of the 

 spermatheca of insects ( 886), 

 inasmuch as it seems to form a receptacle for the fecundating secretion 

 of the male, in which the seminal fluid remains, ready to impregnate the 

 ova as they successively pass its orifice during their expulsion from the 

 body. 



(1062.) The eggs are almost invariably carried about by the female 

 until they are hatched, and in order to effect this, various means are 

 provided. In the Decapoda they are fastened by a stringy secretion to 

 the false feet under the abdomen ; and a female Crab may generally be 

 readily distinguished from a male of the same species by the greater 

 proportionate size of this part of their body. 



(1063.) Many of the Decapod Crustaceans, as, for example, the Cray- 

 fish (Astacus fluviatilis), do not not seem to undergo material alterations 

 of form, but simply moult at certain intervals, throwing off their old 

 integument and acquiring a new covering. Nevertheless, even in the 

 Decapoda it is certain that great metamorphoses take place in the ex- 

 ternal appearance of the young animals. Cavolini long since announced 



Female generative organs of Astavus fiu- 

 viatilis: a,bb, ovaria; c, oviduct; d, external 

 termination of the right oviduct; e, escaped 

 ovum. 



