138 



ROUNDWORMS. PHYLUM NEMATODA 



known as the rect.nn. Ihe fore- and hind-guts are lined bj' in- 

 turned ectodonn, with a prolongation of the outer cuticle, which 

 is shrd with the latter. They have in their walls muscular fibres. 

 The mid-gut is composed solely of a layer of columnar epithehum, 

 with a basement membrane outside it. The food consists of solids 

 and liquids taken up from the contents of the intestine of the host. 

 There is neither vascular nor respiratory system. 



REPRODUCTION 



Fig. ioi.— Muscle fibres of Ascaris. — From Parker and Hasvvell, after Leuckart. 



4 A sincle fibre ■ B several fibres in traDSverse section, with a portion of the ectoderm (below) ; 

 " ' c. Contractile 'part of the fibre ; /, processes ; nu, nucleus ; p, undifferentiated protoplasmic part ot 

 tile fibre. 



The genital organs (Figs. 102 and 103) are of a type peculiar 

 to the Nematoda. They are paired in the female and unpaired 

 in the male, and lie free in the body cavity. The male apparatus 

 is composed of (a) the testis, a long, coiled thread consisting 

 in its anterior part of a solid mass of immature sex-cells, 

 and in its hinder part containing a cord or ' rachis ' in the 

 middle with riper sex-cells attached to it, {b) the vas deferens 

 of much the same width as the testis, (c) the vesicula seminalis, 

 a wider tube, (d) a short, narrow, muscular ejaculatory duct. 

 The spermatozoa are simple rounded cells, which become 

 amceboid when they have been transferred to the female. The 

 "lie organs correspond with those of the male. Each ovary 



