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



remain uncertain whether Nelson's "false eggs" had really 

 escaped fecundation. 



It is by no means our intention to represent this influence of 

 the act of fecundation upon the formation of the chorion as uni- 

 versal. There are Neniatoid worms in which the eggs surround 

 themselves with a perfectly regular chorion, even in the unim- 

 pregnated females, — as, for example, Oxrjuris vermicularis and 

 many others. 



We have turned our attention particularly to the mode in 

 which the fecundation is effected, but without being able to 

 arrive at any positive result. Nothing, especially, could be dis- 

 covered from which it might be concluded with some probability 

 that the zoospermia penetrate into the yelk. It is a recognized 

 principle that a positive observation cannot be subverted by a 

 negative one ; and for this reason we shall by no means declare 

 the statements of Nelson and INleissner to be improbable. We 

 may nevertheless be permitted to subject the investigations of 

 both observers to a sound criticism, in order to see how far they 

 can endure a close examination, and whether they really prove 

 what they profess to do. 



Supposing that the thimble-like corpuscles penetrate into 

 the yelk, the most important question is, whether this penetra- 

 tion takes place in accordance with the description of Nelson 

 or that of Meissner. Nelson found numerous seminal coi*- 

 puscles adhering to the surface of the eggs, which we readily 

 believe, as these corpuscles very easily adhere to foreign objects 

 by means of their flocculent extremity This adhesion to all 

 possible bodies is even the cause of the error into which 

 Bischoff, Leuckart, and Eckhard have fallen. Nelson, however, 

 goes still further, and says that he has seen how the seminal 

 corpuscles pressed-in the surface of the yelk, and finally pene- 

 trated into it from all sides. There is no doubt that Nelson's 

 figure and description are accurate. Nevertheless, it is a ques- 

 tion whether this observer had to do with a natural or with an 

 accidental phenomenon. If we closely examine Nelson's figure, 

 w^e cannot avoid considering the latter as the more probable. It 

 evidently represents crushed eggs, — and that zoospermia should 

 get accidentally into a crushed egg, cannot be considered strange. 

 Thompson has been more careful than his friend : he has cer- 

 tainly observed the adhesion of the seminal corpuscles on the sur- 

 face of the eggs and fissures in the outer layer of the vitellus, but 

 he does not venture to assert that he has seen seminal corpuscles 

 in the vitellus itself, — na}", he does not even believe that these 

 phsenomena must necessarily be brought in connexion with the 

 act of fecundation. It appears to us, however, that Nelson and 

 Thompson made their observations through the walls of the ovi- 



