134 



NEMATHELMIXTIIES 



cretory organs which was not supposed to exist in the lateral 

 canals of the Xematoda. 



The Reproductive Organs. With the exception of the 

 genera Angiostomum, Fclodytcs, and of 

 Jihaldoncma nigrovcnosum, which arc 

 physiologically hermaphrodite and self -im- 

 pregnating, the Xematodes have separate 

 sexes. The males are, as a rule, smaller 

 than the females, and may usually be distin- 

 guished by the posterior end of the body 

 being curved towards the ventral surface ; a 

 genital bursa, and one or more spicules are 

 also peculiar to this sex. Further, the posi- 

 tion of the genital opening differs ; in 

 the male the vas deferens opens on the ven- 

 tral surface of the rectum close to the anus, 

 but the oviduct in the female opens in the 

 ventral middle line, usually near the middle 

 of the body, but sometimes close behind the 

 excretory pore, or in some Strongylidae just 

 in front of the anus. The tail of the male 

 bears very numerous papillae, which are of 

 considerable systematic importance. 



With rare exceptions, e.g. Filaria atten- 

 uata, where it is double, the male reproduc- 

 tive organ consists of a single tube divisible 

 into a testis proper, a vas deferens, a vesicula 

 seminalis, where the spermatozoa are stored 

 up, and a ductus ejaculatorius. The tube 

 stretches through the body in a straight line 

 the dorsal middle line, in the small free-living forms, but is thrown 

 testine ; o-ertfa; "/, ^ n ^ 1P S an( l c il s i u the larger parasitic 

 vas deferens: /(.lateral Xeiuatodes. Within the testis the mother- 

 excretory canals. ,, , . 



cells 01 the spermatozoa are attached to a 



rhachis or axial cord ; the mother-cells divide, and their products 

 ultimately form spermatozoa. The latter have a very peculiar shape ; 

 in accordance with the universal absence of cilia in the Xematoda 

 the spermatozoon has no liagellum, and at first consists of a 

 spherical nucleated cell, on one side of which a cap or covering 

 of some refractive substance appears. The cap elongates and 



FIG. 66. A sccris lurnlri- 

 coides Cloq. <j , natural 

 size, cut open along 



