No. 2.] OOKINESIS. 243 



tradict it in both points. On pages 392-394, Van Beneden 

 formally enumerates the changes exhibited in the protoplasmic 

 substance of the spermatozoon the moment it comes in contact 

 with the egg; and on page 395, he distinctly states that the 

 nucleus undergoes, at the same time, " une modification tres 

 apparente." Nussbaum's statements are a little less explicit; 

 but, so far as they go, confirm those of Van Beneden. But it 

 is only after the expulsion of the second polar globule, accord- 

 ing to Van Beneden (p. 355), that the spermatozoon undergoes 

 *' those modifications which announce the imminence of fecunda- 

 tion," and this statement may possibly have misled Hertwig, 

 A citation, previously made (p. 235), from Van Beneden shows 

 that Hertwig was also mistaken in supposing that the sperma- 

 tozoon remained stationary for a considerable time at the 

 surface of the egg. 



Zacharias (10) fully confirms Van Beneden's statements in 

 regard to the centripetal movement of the spermatic body, and 

 gives, besides, a detailed description of the changes which take 

 place in it before the formation of the second polar globule. 

 In unfertilized eggs the first polar globule is formed, but not 

 the second. This fact shows how erroneous is the idea that 

 the spermatozoon remains passive until after the extrusion 

 of the polar globules. 



III. The Pole of Impregnation. 



The copulation of the sexual cells is attended with very inter- 

 esting ookinetic phenomena. A remarkable example has been 

 described by Fol (6, pp. 91, 249), in the egg of Asterias gla- 

 cialis. The protoplasm rises up at one point in the form of a 

 cone, which continues to elongate until it meets the sperma- 

 tozoon on its way through the mucous envelope ("oolemma"). 

 The height of the cone depends on the rapidity with which 

 the spermatozoon advances. If it progresses slowly, the cone 

 may attain a height equal to half the thickness of the oolemma. 

 As soon as contact is established, the cone begins to shorten, 

 but rarely disappears entirely. Its summit, terminating in the 

 remnant of the tail of the spermatozoon, usually remains above 

 the surface of the o.^^., and soon becomes the point of de- 

 parture for a new cone, — the "cone of exudation," — which 

 is supposed to arise by expulsion of the vitellus. 



