3 22 



THE ROUND WORMS 



These parasites can be seen with an ordinary magnifying glass. With higher 

 powers the oesophagus has the appearance of a serrated line instead of an cesophageal 

 bulb. The male is about 40;* broad and has a prominent testicular enlargement 

 filling the posterior extremity. The female is about 6opt broad and has a rounded 

 posterior extremity with a prominent slit-like cloaca. It is in this posterior extrem- 

 ity that the female increases in size as she becomes filled with eggs. The vulva is in 

 the anterior third. After fertilization of the females the males die, and the females 

 bore into the intestinal mucosa and begin to produce embryos to the number of 

 more than 1000 each. These gain access to the lymph channels and are distributed 



2. Stronyytoides etercoralia. (parasitic.) 



1. Trichinella spiralis. A-Mhenooenetic female 



B-Rhabditifirm embryo , 



7- Tern idena 'i. b-femole c-poftericr 

 demlnutuS nirtmity of mate, (spiiules) 

 d*e- anterior extremities. 



brumpti 



FIG. 74. Some of the human nematodes. 



by the blood-stream to the striated muscles. Embryos reaching other tissues fail to 

 develop. 



It is about ten days before they reach the muscle. In the muscle they become 

 encysted as the oval lemon-shaped areas containing coiled-up embryos that every- 

 one is familiar with. These oval areas are about 450 X 250/1 and have a chitinous 

 capsule. 



The encysted trichinae are found chiefly in the muscle fibers of the tongue and 

 diaphragm and may remain alive as long as ten to twenty years; finally, however, 

 the cyst undergoes calcareous infiltration and the embryo dies. 



When uncoiled the embryo is about i mm. long with the mouth at the attenu- 

 ated end. Among cannibals it would be easy to keep the cycle going by eating 

 improperly cooked or raw human meat, the parasite being thus transmitted. 



