OXYUBTS VEBMK'ULARTS. 369 



siderably under the action of acetic acid, acquiring a size three or 

 four times greater than that of the egg. The constitution of this 

 chorion is perfectly identical in the eggs both before and after 

 impregnation. It is, nevertheless, easy at first sight to know 

 "whether or not we have to deal with a fecundated egg. In the 

 impregnated females the uteri are filled with thousands of ova, 

 each one of which encloses an embr^^o already well formed. The 

 ventral surface of the embryo and its tail face, without exception, 

 the flattened side of the egg. The embryo is very broad in the 

 body, and occupies all the interior space. An embryo such as 

 Kiichenmeister has represented under the form of a small filiform 

 worm folded on itself, and only occupying a very small part of 

 the cavity of the egg, is never to be seen. In the non-fecundated 

 females, on the other hand, the uteri are filled with eggs, which, 

 instead of the embryo, enclose a non-segmented yelk furnished 

 with a large germinal vesicle. This vesicle is not visible so long 

 as the eggs have the form of thin disks ; it only shows itself when 

 the egg begins to acquire an elliptical form in the oviduct. It is, 

 however, probable that this vesicle is the same which was origi- 

 nally visible in the ovary." The chorion itself is homogeneous, 

 but in an allied species (Oxyuris sjpirotheca) Gyoery and Claperede 

 have discovered that this egg-covering consists of spirally coiled 

 bands resembling the tracheal spiral fibre of an insect. I may 

 here also mention that I have observed precisely similar appear- 

 ances in the chorion-like investment surrounding a minute nema- 

 tode larva lodged in the intestinal mucous membrane of a heron 

 {Ardea). This may help us to establish the genetic relations of the 

 species in question. 



Respecting the migrations of the larvae, I am not aware that 

 anything very definite is yet known. I have introduced the eggs con- 

 taining embryos into various animals, but have not yet succeeded in 

 rearing young Oxyurides. I have also introduced them into the 

 pulpy parenchyma of apples and pears, but I have not been able to 

 satisfy myself that any of the young nematodes which I subsequently 



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