INTRODUCTION. 17 



They consist of a pair of testes, a long vas deferens 

 leading posteriorly from them, and a pair of spermato- 

 phore sacs in the genital segment. The testes are 

 oval bodies situated in a corresponding position to the 

 ovaries in the female. The spermatophore is an oval 

 body of a pale yellow colour filled with sperms. It is 

 expelled from an opening near the posterior end of the 

 genital segment. A short cement-gland is situated in 

 the segment and is furnished with a duct which is 

 connected with the anterior end of the sac. 



The female is fertilized early in life by the male 

 attaching spermatophores to the vulvae. The contents 

 of these bodies appear to suffice for the fertilization of 

 all the eggs which the female produces during its life. 

 The genital segment of an unfertilized female is very 

 small. It is only about one-fifth the size it attains in 

 the mature condition. The eggs are fertilized from 

 the store of sperms as they leave the oviduct, and are 

 then enclosed in a thin chitinous tube which gradually 

 lengthens as the eggs are expelled. This tube is the 

 ovisac, and the eggs are arranged in a single column 

 sometimes exceeding the length of the animal. The 

 whole of the embryos in the tube practically hatch at 

 once when the development is completed. The embryos 

 hatch as nauplii about 0*46 mm. in length. The 

 nauplii are free-swimmers for a time and then settle 

 down as Cyclops forms upon their host. As soon as 

 the cyclops form settles it develops a thin chitinous 

 filament from a median gland in the anterior end of 

 the cephalo-thorax. The filament is inserted in the 

 tissues of the host and the young parasite becomes 

 firmly anchored. A median sucker which assists in the 

 attachment is also developed at the same time. The 

 genus Chalimus, described by Burmeister in 1831, was 



VOL. i. 2 



