VI 



PHYLUM NEMATHELMINTHES 



285 



int 



compartment containing the intestine and the nerve-cord, a pair 

 of large lateral compartments containing the ovaries, and a pair 

 of small dorso-median canals which act as oviducts. It is stated 

 that the median ventral compartment acts as an excretory canal 

 and opens posteriorly along with the 

 oviducts : in the Gordiacea there are no 

 lateral excretory canals like those of 

 Ascaris and the other typical Nema- 

 todes 



In the Nematoidea the nervous system 

 has the structure already described in 

 Ascaris : it is, however, apparently ab- 

 sent in some free-living forms. But in 

 Gordius it is much more highly de- 

 veloped : the pharyngeal ring is of great 

 thickness and is continued into a single 

 ventral cord (Fig. 230, bm.), containing 

 nerve-cells, which compares very well in 

 size with the corresponding organ in the 

 higher Worms. Eye-spots have also been 

 described in the sexual form of Gordius. 



The reproductive organs in all the 

 Nematoidea resemble those of Ascaris, 

 the only important variation depending 

 upon the fact that in the smaller forms 

 the entire genital tube (gonad plus 

 gonoduct)is short and not coiled (Fig. 231, 

 ts. and v. df.\ A few forms are herma- 

 phrodite, but, instead of having a double 

 set of reproductive organs, as in Plat odes, 

 organs of the ordinary female nematode 

 type are present, and the gonads produce 

 first sperms and afterwards ova. Such 

 animals are said to be protandrous (male 

 products ripe first), and self-impregnation 

 is as effectually prevented as if the organs 

 of the two sexes were distinct. A totally 

 different arrangement is met with in the 

 Gordiacea : the female having numerous 

 pairs of ovaries (Fig. 232, A, c,vy.) arranged 

 segmentally and attached to one of the 

 partitions (mes.) of the body-cavity. The 

 ripe eggs are discharged into large egg- sacs, formed by the 

 lateral compartments of the body-cavity, and finally make their 

 way into the medio -dorsal compartments which act as uteri (C, 

 ut.) and are continued posteriorly by short vaginae (vag.) into a 

 median chamber. The latter opens externally, and also receives 



FIG. 231. Oxyuris, from the 

 right side. gz. gizzard ; int. 

 intestine ; ph pharynx ; 

 pn. s. penial sitse ; ts. testis ; 

 r. >Jf. vas defereiis. (From 

 Shipley, after Galeb.) 



