188 M. E. Claparede on the Formation of the Egg 



lent structure when this corpuscle reaches the female generative 

 organs, and becomes the flocculent end of the thimble-like zoo- 

 spermion, has not indeed been as yet observed directly. But 

 the probability of this change becomes elevated into certainty 

 by the fact, that we have directly observed an exactly similar 

 process in the seminal corpuscles of Strongijlus auricularis. 



It is deserving of notice that these facts were not entirely un- 

 known to Bischoff. He has had an Ascaris mystax in his hands 

 the eggs* of which were to all appearance unfecuudated, and 

 its sexual organs also contained none of the so-called epithelial 

 conules. Nevertheless, Bischoff firmly retained his opinion, and 

 supposed that the conules were wanting because the female was 

 immature. He thinks to find a proof of this in the fact that the 

 eggs appeared quite otherwise than in other cases ; the chorion 

 was not granular as usual, but lamellose and thin. This is no 

 proof; but nevertheless the observation is interesting, as we shall 

 show immediately that in many Nematoidea the want of fecun- 

 dation superinduces the formation of an abnormal chorion. 



That the unfertilized Ascarides observed by us were not imma- 

 ture, is perfectly certain. j\Iost of them were very large; many 

 of them even very considerably exceeded the maximum of length 

 to which this species is otherwise restricted. 



The fate of the ova in Ascaris suilla is different, according as 

 they are fertilized or not. We shall in the first place consider 

 the fertilized egg. 



As soon as the egg has passed the spot where the fertilization 

 takes place, it surrounds itself with a distinct membrane. This 

 is no new foi'mation, no structure secreted from the tube; it 

 rather appears to us that this membrane is only produced by a 

 sharper differentiation of the outer denser layer which has already 

 been referred to. At any rate, the formation of this membrane 

 is no immediate consequence of fecundation, for it also occurs in 

 the unimpregnated female. But in the latter this membrane 

 appeared to be thinner and more delicate. Around this mem- 

 brane a second is formed, the chorion, probably secreted by the 

 walls of the genital tube. This chorion attains a considerable 

 thickness, and is smooth on the surface. At the same time, a 

 molecular change shows itself in the interior of the yelk. Be- 

 fore fecundation the latter was perfectly opake, and consequently 

 appeared nearly black under the microscope. But after fertili- 

 zation the vitelline granules gradually become less refractive, 

 and the yelk thus appears paler and more transparent. At the 

 same time a clear vesicle becomes visible in the midst of it. 



In the unimpregnated female the e^^ does not j)roperly sur- 



* Ueber Ei- unci J?amenbi Idling und Befriichtung bei Ascaris mystax. 

 Zeitscbr. liir wiss. Zool., February 1866. 



