L34 



NEMATHELMINTHES 



CHAI 



L.a 



7i-i 



X 



cretory organs which was not supposed to exist in the laten 



canals of the Nematoda. 



The Reproductive Organs. With the exception of the 

 genera Angiostomum, Pelodytes, and of 

 Bhabdonema nigrovenosum, which are 

 physiologically hermaphrodite and self- im- 

 pregnating, the Nematodes have separate 

 sexes. The males are, as a rule, smaller 

 than the females, and may usually be distil 

 guished by the posterior end of the bod] 

 being curved towards the ventral surface ; 

 genital bursa, and one or more spicules art 

 often found in this sex. Further, the posi- 

 tion of the genital opening differs ; ii 

 the male the vas deferens opens on the ven- 

 tral surface of the rectum close to the anui 

 but the oviduct in the female opens in tht 

 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 

 in the small free-living forms, but is thrown 

 into loops and coils in the larger parasitic 

 Nematodes. Within the testis the mother- 

 cells of 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 Nematoda 



B 



Fig. 66. Ascaris lumbri- 

 co ides Cloq. <$, natural 

 size, cut open along 

 the dorsal middle line. 

 a, Oesophagus ; b, in- 

 testine ; c, testis ; d, 

 vas deferens : h, lateral 

 excretory canals. 



the spermatozoon has no flagellum, 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 



