26 ON PARASITES. 



distinct. The Nematoidea occurriag in the human subject are Tricho- 

 cephalus dispar, Oxyuris vermicularis, Strongylus gigas, Filaria 

 medinensis, Ascaris lumbricoides, Spiraptera hominis, Ancyclostoma 

 duodenale. 



T richocephalus dispar. 



The body is long and formed of two parts. The anterior is quite 

 thin and thread like ; the posterior is thick and contains the genital 

 organs. The male is smaller than the female. The testicle and 

 spermatic cord are simple. The latter opens with the intestine into 

 a common cloaca. The penis is simple. 



The caudal extremity is supplied with an auxiliary copulatory 

 organ. The zoosperms are globular. 



The female is straighter, somewhat broader, less elastic and flexible 

 than the male. The caudal extremity is acuminate. The vagina is 

 muscular and opens on the ventral surface, both uterus and ovary are 

 simple. The ovules are brownish — oblong — provided at each extremity 

 with a small but distinct wart-like prominence. Generation — oviparous. 



Oxyuris. 



The body is cylindrical or fusiform. The head is unarmed — the 

 mouth is terminal orbicular or triangular. The sesophagus is muscu- 

 lar. The gastric cavity is triangular. The intestine in the female 

 opens anterior to the acuminate tail. In the male it opens in the 

 centre of the tail which is obtuse. 



The males are almost microscopic in size, mostly seen curled in 

 spirals blunted at the posterior extremity. The females are larger than 

 the males and have a sharp tail ; a bilocular uterus with two ovaries, 

 the vagina always in the anterior part of the body, where the external 

 genital orifice is also situated. Length 5-6 lines. 



This worm inhabits the larger intestines of children, causing some- 

 times much irritation. 



Ascaris. 



The body is white, sub-cylindrical, attenuated on each side, marked 

 with four whitish longitudinal lines. The skin is transversely striated. 

 The anterior extremity is marked by three convex or hemispherical 

 valves. They serve as lips to aid the animal in fixing itself on the 

 spot where it is to derive its nourishment. 



The sesophagus is strongly muscular, cylindrical or claviform. The 



