14 M. F. Plateau on the Freshwater Crustacea of Belgium. 



tory feet, with enormous respiratory vesicles, and with scarcely 

 any setse. 6. The male and female reproductive apparatus. 

 I have discovered the male of L. trigonellus and rediscovered 

 that of L. lamellatus ; they differ from the females by their 

 smaller size, their more elongated body, and by the consider- 

 able size of the antenna3 of the first pair. The essential part 

 of the reproductive organs consists of a membranous sac on the 

 inner surface of the penultimate joint of the tail, containing 

 two sacciform glands, slightly constricted in the middle, and 

 each furnished with a wide and short excretory duct ; these 

 two ducts open at the base of the caudal lamina. Sperm ato- 

 zoids are frequently met with in the fecundated females ; 

 these are, like those of the Daphnice, fusiform bodies with a 

 membranous border. The female apparatus of the Lyncei 

 greatly resembles that of the Da/phnicB ; the winter eggs, 

 which the incubatory cavity contains at certain periods of the 

 year, are not enclosed in a common einhipinum^ but there is a 

 membranous capsule or distinct ephippium for each e^^. 



Straus Diirckheim, in a memoir which has justly become 

 celebrated, has given in much detail the anatomy of Cypris 

 fusca ; but he had never seen anything but ovaries in the in- 

 dividuals which he examined, which led him, like Ramdohr, 

 Treviranus, and many others, to regard the Cyprides as her- 

 maphrodites. In 1850, M. Zenker indicated the existence of 

 distinct males. In 1854 he described in detail their sexual 

 organs — consisting of two testes represented by masses of 

 csecal tubes, of two cylindrical glands of very complicated 

 structure [glondida mucosce), the secretion from which serves 

 to form the spermatophores, and, lastly, of two corneous sacs, 

 enclosing a corneous penis and hooks, or excitative organs, 

 which are also corneous. 



Having myself rediscovered the males of Cypris monacha^owdi 

 studied great numbers of the females and young of other species, 

 I have been able to verify most of M. Zenker's observations, and 

 to add some new facts to those made knoAvn by him. 



These new facts are as follows : — The mucus-glands of the 

 male C. monacha^ contrary to what is stated by M. Zenker, 

 present a temporary sacciform prolongation, which is some- 

 times found filled with spermatophores. The place of forma- 

 tion of the spermatophores is not the deferent canal of each 

 testis, but the central canal of the corresponding mucus-gland. 

 The free spermatozoids (that is to say, destitute of the envelopes 

 of the spermatophore) may be classed in two groups : those of 

 the first group are filiform, without dilatation of any kind; and 

 those of the second, which are met with in C. ovum, and per- 

 haps in C. punctata, arc furnished at one of their extremities 



