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



tory feet, with enormous respiratory vesicles, and with scarcely 

 any setge. 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 antennge 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. Spermato- 

 zoids are frequently met with in the fecundated females ; 

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

 membranous border. The female apparatus of the Lyncei 

 greatly resembles that of the Daphnice] the winter eggs, 

 which the incubatory cavity contains at certain periods of the 

 year, are not enclosed in a common ephippium, but there is a 

 membranous capsule or distinct ephippium for each egg. 



Straus Durekheim, in a memoir which has justly become 

 celebrated, has given in much detail the anatomy of Gypris 

 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 Uyprides 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 

 caBcal tubes, of two cylindrical glands of very complicated 

 structure (glandules mucosa), 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 monaclia, and 

 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 known by him. 



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

 male C. monaclia, 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 G. ovum, and per- 

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



