CRUSTACEANS. 611 



the form of two blind sacs. Sometimes, as in the decapods, these 

 have a more glandular aspect, and consist of an aggregate of many 

 follicles. In the long-tailed ten-footed crustaceans the two testes 

 form a single three-lobed body, though there are two vasa deferentia. 

 These efferent tubes open in these crustaceans, as also in the short- 

 tailed or crabs, at the base of the feet of the fifth pair. In these 

 mimals the external male organs of copulation have horny accessory 

 >rgans attached to the first two abdominal rings which support the 

 )enis in copulation, and which as to their function may be compared 

 th the little bone that occurs in this part in some mammals. 



The eggs of crustaceans after they have been laid often continue 

 tached to different parts of the parent's body, and there advance 

 further development. In the Ontscides, and many other crusta- 

 ans, the development takes place in a brooding cavity at the 

 der surface of the anterior part of the body, where it is covered 



a different number, commonly by five pairs, of ventral plates 

 .ng on one another like roof-tiles 1 . In DapJinia the eggs remain 



some time in a cavity beneath the shell on the back ; in Cyclops 

 sy are carried about in two bunches by the female at the base of 

 e abdomen. The same is observed in many parasitic crustaceans. 



others they are attached to the feet by an adhesive fluid hardened 

 to threads; in the ten-footed crustaceans, to the feet of the abdo- 

 3n or of the so-called tail. Other crustaceans divest themselves 



their eggs without bearing them about on their body, and attach 

 em to other objects. Thus the female of Arguing foliaceus affixes 

 r numerous eggs (100 200) by means of a viscid covering to 

 mes 2 . Cypris also lays her eggs upon different bodies under 

 iter, often in heaps of a hundred, which she covers with a green 

 ready matter 3 . 



The egg of crustaceans, whilst still in the ovary, consists of the 

 Ik, the germ vesicle, and the vitelline membrane. The yolk is 

 ghtly fluid, and consists of shapeless fat-particles and cells, with 

 ly a small quantity of albuminous fluid. The germ-vesicle, 

 lich again includes different small vesicles (germ-spots), disappears 

 ter impregnation, as soon as the egg enters the oviduct. Here, 011 

 e other hand, it receives an external covering, a chorion, formed 



1 TREVIRANUS Verm. Schr. i. Tab. ix. figs. 51, 52. 



8 JURINE, 1. 1. pp. 452, 453. 3 STRAUS, Mem. du Mus. vn. p. 54. 



392 



