MUSEUM OF COMPARATIVE ZOOLOGY. 483 



In the " General Part " of this paper Hertwig considers, among other 

 things, the grounds for maintaining the morphological identity of the 

 " Spermakern " with the body (nucleus) of the spermatozoon, rather 

 than the dissolution of the spermatozoon and subsequent re-collection of 

 its substance into a male pronucleus, as held by Ed. van Beneden and 

 Strasburger. They are : — 



1. In the conifers the possibility that the fine membrane of the apex 

 of the pollen tube is partly dissolved away, cannot be excluded. 



2. In Hirudinea, mammals, etc., the vitelline membrane can present 

 no obstacle to the penetration of spermatozoa, inasmuch as many have 

 been observed within the membrane. 



3. A difference in size between the Spermakern and the body of the 

 spermatozoon is not evidence against their identity, since the former is 

 by direct observation known to increase in size before copulation with 

 the egg nucleus. 



4. In Toxopneustes there is an interval of only a few minutes between 

 the time of artificial fertilization and the appearance of the sperm nu- 

 cleus. It is improbable that a solution and re-forraation takes place in 

 this short interval, nor is there any motive to such an widirect procedure. 



5. The existence of a fine filament seen in Toxopneustes to extend 

 from the sperm nucleus beyond the periphery of the egg, which is to be 

 interpreted as the cilium of the spermatozoon. 



Perez (Vl) gives in a note the results of his attempt to verify on 

 Echinus esculentus Fol's recently published account of the phenomena 

 of fecundation. In two cases he observed the protuberance of the sur- 

 face of the Ggg, which Fol considers due to an " attraction a distance " 

 exercised by a spermatozoon, but is unable to attribute to it the least im- 

 portance. In one case there was no spermatozoon facing the elevation ; 

 in the other, a spermatozoon, after remaining immovable for some seconds 

 in the middle of the thickness of the mucous layer, advanced actively 

 to the summit of the elevation ; but there was no delicate prolongation 

 of the elevation toward the spermatozoon, nor did the latter glide into 

 the yolk, — it remained fixed at the surface. Scarcely was this eff'ected, 

 when a second, following the same course as the first, traversed the 

 mucous layer " with two or three leaps," and joined the surface of the 

 minute elevation. Two others followed, but reached only the middle of 

 the layer. Neither of the first two entered the egg, but with the eleva- 

 tion of the previously existing vitelline membrane, which soon followed, 

 were borne a considerable distance from the yolk, which was, neverthe- 

 less, now fertilized. 



