128 ZOOLOGY 



The testis opens into a vesicula seminalis of a much 

 greater diameter than the testis tube, its lining epithelium 

 throws out processes into the lumen which resemble pseudo- 

 podia. These possibly perform the same function as the cilia 

 which usually occur in the vesicula seminalis of other animals, 

 cilia being entirely unknown in Nematodes. 



The vesicula seminalis opens into a ductus ejaculatorius, 

 with muscular walls. This ductus opens on the dorsal side 

 of the rectum. On each side of it is a sac containing a 

 chitinous spicule which is protrusible, and is doubtless used 

 in copulation. 



The female organs are double, and consist of ovaries, 

 oviducts, uteri, and a vagina, the latter opening on the 

 ventral middle Une. The ovary consists of a tube in which 

 the egg cells are formed in enormous numbers as stalked 

 structures borne on a rachis. The oviduct differs from the 

 ovary only in containing free ova, it leads on each side into a 

 uterus in which numerous spermatozoa are found, and where 

 the fertilisation of the ovum takes place. The two uteri 

 unite, and open by means of a short vagina to the exterior. 



The eggs are laid in millions, each surrounded by a smooth 

 shell. The embryos develope in water or in damp earth, and 

 are probably introduced into their human host by the drinking 

 of dirty water. 



The majority of Nematodes are parasitic, at any rate during 

 a portion of their life, but a good many lead a free existence in 

 damp earth, moss, and decaying matter, or in salt or fresh 

 water. These are mostly minute forms, and are capable of 

 withstanding a considerable amount of desiccation. The free- 

 living forms, with certain others that inhabit plants, are 

 included in the family Anguillulidae. 



Tylenchus tritici does great damage to corn crops, its 

 presence leads to the grains of corn being replaced by a dark 

 brown gall. Inside this gall a small cluster of these minute 

 worms are found. When one of the galls is sown with the 

 seed, and rain foUows, the parasites leave the gall and infest 

 the young plants. The parasites pair within the gall on the 

 corn ear, and eggs are laid within the gall. 



Amongst the Nematodes which are parasitic in animals. 



