ANATOMY OF THE NEMATODES 



269 



cephalus, Trichinella, &c.), however, special excretory organs are 

 lacking ; possibly the cutaneous glands, which are in these species 

 generally powerfully developed, replace these organs. 1 



SEXUAL ORGANS. With the exception of a few species, the 

 Nematodes are sexually differentiated. - 



(a) FEMALE SEXUAL ORGANS. The sexual .orifice (vulva), sur- 

 rounded by thick labia, is, as a rule, ventral and situated in the 

 middle of the body, or a little more forward, rarely further back. It 

 leads into a short vagina, continued by the two uteri, which may be 

 long or short ; the long filiform ovaries are contiguous to them 

 (fig. 186). In smaller species one of the uteri, with its ovary, 

 extends towards the front, the other towards the 

 back. In larger species both the uteri and ovaries 

 extend backwards (parallel), the latter attaining a 

 considerable length, so that they form many con- 

 volutions in the body. The entire apparatus lies 

 within the abdominal cavity, and in some species 

 ~ 7 - (for instance, Trichinella) is single. 



At the blind end of the ovary there is a cumulus 

 oophorus, i.e., a mass of protoplasm with numerous 

 nuclei that multiply continuously. Gradually the nuclei 

 arrange themselves in longitudinal rows (fig. 187) and 

 the protoplasm commences to leave the periphery and 

 surround each nucleus. The nearer to the uterus the 

 more progressive is this loosening process, until club- 

 shaped cells each containing a nucleus are developed. 

 The most slender end of each, however, is still attached 

 to an axial fibre of protoplasm, the rhachis ; probably 

 this has some connection with the nutrition of the ova. 

 Finally the ova fall off and reach the uterus, where 

 they are fertilised and enclosed in shells. 



(b) MALE SEXUAL ORGANS. There is never 

 more than one testis (fig. 188), which is a 

 straight or sinuous tube of the same con- 

 struction as an ovary, and in which the sper- 

 matic spore capsules originate in the same manner 

 as the ova. In the same way as the ovarv 



Ov. 



FIG. 1 86. Cen- 

 tral part of the body 

 of the rhabditis 

 form ' of Rhabdo- 

 nema nigrovenosum 

 with female geni- 

 talia lying on its 

 side. (Magnified.) 

 /., intestine; G., 

 genital orifice (vul- 

 va) ; Ov., ovarium ; 

 lit., uterus. 



1 Jagerskiold, L. A., " Beitr. 7. Kenntn. d. Nemat." (I.e.) " Biischclf. Org. b. Asc." 

 (I.e.) " Weit. Beitr. z. Kenntn. d. Nemat." (I.e.). Hamann, O, " Die Nemathelm., II., Jena, 

 1895. Nassonow, N. (I.e.). Cobb, N. A., " Oxyuris-laYua; hatch, in the hum. stow." 

 (Proc. Linn. Soc., N. S. Wales, 1891 [2], v., p. 168), and other authors. 



'Nedkoff, P., " Ueb. d. Metamorph. d. Geschlechtsapp. b. Ascar. nigroven., In.-Diss. 

 Leipzig, 1897. 



