388 CRUSTACEA ENTOMOSTRACA. 



into complex folds. The part of the vas deferens nearer the 

 opening has a chitinous wall, and at its commencement a 

 peculiar ejaculatory apparatus is situated which in the fresh- 

 water forms is a large and complex organ. This was formerly 

 known as the " mucous gland." At its termination the vas 

 deferens traverses the corresponding half of the (paired) penis, 

 the end of it being protrusible. In Halocypridae and Poly- 

 copidae the penis is traversed by the vas deferens but is single, 

 and situated to one side of the middle line. The spermatozoa 

 are very long in some species, in Pontocypris monstrosa they 

 are, according to Miiller, 5-7 mm. in length, or 8-10 times as 

 long as the body of the animal. The female of Cypris 

 possesses two ovarian tubes which project between the la- 

 mellae of the shell (cf. Fig. 253), two receptacula seminis, and 

 the same number of genital openings at the base of the abdomen. 

 As in the Copepoda the receptacula seminis are often provided 

 with two ducts ; one by which the spermatozoa are introduced, 

 and the other communicating with the oviduct. 



In addition to the sexual characters noted above differences 

 in the shape of the shell, and the richer endowment of the 

 male with sensory organs may be noted. 



Development. The greater number of Ostracoda lay eggs 

 which they either attach to water-plants (Cypris} or, as in 

 Cypridina, carry about with them between the shell valves until 

 the young are hatched. Parthenogenesis has been recognized as 

 occurring among the Cypridae by Weismann and by G. W. 

 Miiller. According to Woltereck * it is, in some species, of the 

 kind found in the Daphnidae, in which a number of partheno- 

 genetic generations succeed one another during the summer, to 

 be followed in the autumn by a sexual generation. In Cypris 

 reptans however the sexual generation has never been seen. 

 Cultures of this species have been under observation for eighteen 

 years in the Freiburg laboratory, yet a male has never been 

 recognized. 



The free development of Cypris consists of a complicated 

 metamorphosis. The larvae, when hatched, possess, like 

 nauplius larvae, only three pairs of appendages, but they are 

 strongly compressed laterally, and are already enclosed in a thin 



* R. Woltereck Zur Bildung und Entwickelung d. Ostrakoden Eies, 

 Zeit. /. wiss. ZooL, Bd. 64 (1898), p. 596. 



