DIAGNOSIS OF ENTOZOA 177 



yellow or brown. The egg is variable in size and shape, 

 sometimes nearly spherical, at others markedly oval. The 

 egg-contents are an undivided mass of protoplasm, but in 

 unfertilized eggs there are numerous retractile globules 

 throughout the egg-contents. 



Trichocephalus dispar is a barrel-shaped egg of a yellow- 

 brown colour. There is an opening plugged with mucus 

 at each end. The egg-contents are an undivided mass 

 of protoplasm. 



The eggs of Ankylostomum duodenale and Necator 

 americanus have a very thin transparent capsule. The 

 egg-contents have already commenced to develop, so that 

 they are divided into two or four masses of protoplasm, 

 and if the faeces have been kept may be divided into eight 

 or more masses, and if kept twenty-four hours some 

 of the eggs will contain worm-like embryos. Careful 

 measurements of uncompressed eggs are required to 

 differentiate between the eggs of these worms. 



The Oxyuris vermicularis rarely passes eggs before 

 leaving the intestine. These eggs have a thicker trans- 

 parent capsule than the ankylostome ; usually one side 

 of the egg is flattened, and at the time the fasces are 

 passed the contents of the egg have developed into a 

 vermiform embryo. 



Strongyloides intestinalis is recognized by the free 

 embryos which are passed, not by eggs. These embryos 

 are in active movement and in a slide of semi-fluid or 

 pasty consistence clear tracks are left wherever the 

 embryos have wandered, so that even in small infections 

 the embryos can readily be tracked. No other living 

 embryos are found in the freshly passed stool, but in a 

 motion that has been kept for twenty-four hours or more 

 they might be confused with larval ankylostomes, which 

 are much the same size. They can be distinguished from 

 each other by the oesophagus, which in the ankylostome 

 larvae has a definite globular dilation close to the mouth, 

 which is not present in that of S. intestinalis. 



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