368 ENTOZOA. 



tube consists of a dense fibrous membrane, being directed obliquely 

 downwards with a slight curvature. 



Development. — This is a subject of great importance, inasmuch 

 as our knowledge of the entire life-history of Oxyuris vermicularis 

 may eventually lead us to adopt some plan by which its access to 

 our bodies may be prevented. At present we know very little ; 

 but it is generally supposed that the adult animal may be reared 

 from the egg in one and the same bearer. I believe this notion to 

 be entirely fallacious ; yet, on this hypothesis, Kiichenmeister has 

 asserted that " the emigration of a single pregnant female Oxyuris 

 is sufficient to explain the infection of entire families." Kiichen- 

 meister, indeed, does not appear to have seen the embryos of 

 Oxyuris, for he says that after keeping the eggs for six months in 

 water, he could discover neither mature embryos, nor a distinct 

 segmentation. Very different, however, has been my own experience 

 in this respect, for not only have I constantly found the ova in 

 impregnated oxyurides in all stages of yelk-segmentation, but, in a 

 very considerable proportion of the fresh specimens, I have almost 

 invariably discovered well-formed, tadpole-shaped embryos. With 

 these embryos I have conducted a variety of experiments, but at 

 present the results are chiefly of a negative character. 



The only author who appears to me to have given a correct 

 figure and description of the embryo as it appears in the egg, is 

 Claperede. In his scholarly memoir, " De la Formation et de 

 la Fecondation des CEufs chez les Vers Nematodes," he writes, in 

 reference to the ova of Oxyuris vermicularis, as follows : — " The egg, 

 which exhibits the form of a very narrow disk in the ovary, acquires 

 the shape of an elongated elhpsoid in the oviduct, and at the 

 surface differentiates itself into a very thick viteUine membrane. 

 Then it forms a strong and resisting chorion, which imparts to 

 the egg an outline similar to that of a bridge's span. It has an 

 oval figure flattened at one of its sides. This chorion is very 

 fragile. It frequently gives way under slight pressure from the 

 thin plate of glass which covers the object. It extends itself con- 



