THE ROUND WORMS 



rule. 



The cuticle is formed by the underlying ectoderm which is, as a rule, 

 markedly developed in four ridges which divide the body into quad- 

 rants. Within the ectoderm is the body cavity, a space in which the 

 reproductive organs lie in a clear fluid. The excretory system usually 

 consists of two tubes which discharge near the head. 



While the alimentary canal is more or less tube like in appearance it shows near 

 the mouth a muscular oesophagus with a bulb-like expansion at the commencement 

 of the remainder of the intestinal tract. There is a nerve ring around the oesophagus. 



The testis and ovary are generally tube like. The sexes are, as a rule, separate. 

 The male can usually be recognized by its smaller size, its curved or curled posterior 

 end, and at times exhibiting an umbrella-like expansion the copulatory bursa. 

 The spicules, chitinous copulatory structures, may be observed drawn up in the worm 

 or projected out of the cloaca. The genital opening of the female is ventral and 

 usually about the mid-point; that of the male is close to the anus. 



Certain papillae in the region of the anus are valuable in differentiation. As a 

 rule, nematodes develop in damp earth from the eggs as rhabditiform larvae. Very 

 few nematodes are viviparous (Filaria, Trichinella) being usually oviparous (As- 

 caris) less frequently ovo viviparous (Oxyuris). 



The families Gnathostomidae and Anguillulidae are of very little 

 importance in human parasitology. Gnathostoma siamense was once 

 found in a breast tumor and Rhabditis pellio once in the urine. 



Anguillula aceti, the vinegar eel, has been reported from the genito-urinary tract 

 several times. Such cases can be explained by the prior contamination of the urine 

 bottle or by the use on the part of the patient of a vinegar vaginal douche. The 

 genera Rhabditis and Anguillula belong to the family Anguillulidae. 



A case of infection with a small nematode found in the papules of a skin infection, 

 in a French boy is recorded as due to Rhabditis niellyi. The present view is that 

 the parasites were embryos of A. duodenale, boring into the skin. 



ANGIOSTOMID,E 



In this family we have heterogenesis. 



Strongyloides stercoralis. This parasite was formerly thought 

 to be the cause of Cochin-China diarrhoea. It presents two genera- 

 tions: i. Parasitical or intestinal form. 2. The free living or faecal 

 form. 



i. The intestinal form (also known as Anguillula intestinaHs} is represented only 

 by females. These are about ^2 inch (2 mm.) long and reproduce partheno- 

 genetically. They have a pointed, four-lipped mouth, and a filariform oesophagus 

 which extends along the anterior fourth of the body. The anus is situated near the 

 sharpened posterior end, the vulva about the lower third of the body. The uterus 

 contains a row of eight to 10 elliptical eggs which stand out prominently in the pos- 



