480 BULLETIN OF THE 



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absence of such convincing proof of their nature as that soon brought 

 forward by another observer. 



The fecundation of Asterias glacialis, as described by Fol ('77", p. 359), 

 is of great interest. The spermatozoa come in contact with the egg and 

 remain with the " body " imbedded in the m.ucous envelope which sur- 

 rounds the yolk. When one of them has succeeded in traversing half 

 the thickness of this envelope the protoplasm of the yolk accumulates 

 at the nearest point of its surface as a thin hyaline layer, which soon 

 rises in the centre in the form of a boss. This next changes to the 

 shape of a cone, and soon a fine thread of protoplasm establishes a 

 connection between the summit of the cone and the body of the sperma- 

 tozoon. The latter elongates, and, as it were, glides into the yolk, the 

 cue alone remaining outside, where it can be distinguished for some 

 time. Meanwhile the superficial hyaline layer increases in extent and 

 finally envelops the whole yolk. At the moment the connection with 

 the spermatozoon is established, this layer becomes clearly differentiated 

 and begins to detach itself from the vitellus as a vitelline membrane. 

 This differentiation commences at the point of fecundation, where there 

 is formed a sort of minute crater, and thence passes entirely around the 

 yolk. In eggs that are quite mature and fresh, these changes succeed 

 each other with such rapidity that all spermatozoa which are a few 

 seconds behind the first are debarred access to the vitellus. Fol ex- 

 presses the opinion that normally fecundation is accomplished in the 

 starfish by a single spermatozoon ; with the sea-urchin this fact is evi- 

 dent. The point of penetration becomes the centre of a male aster ; in 

 the middle of which a mass is formed (the male pronucleus) which fuses 

 with the female pronucleus as in the case of the sea-urchin. The 

 spermatozoon exercises an attractive influence at a distance, as well as 

 when in contact with the vitellus. 



Toward the- close of the constriction which produces the first polar 

 globule in Nephelis, 0. Hertwig ('77) has observed that a small homo- 

 geneous area, surrounded by radially arranged yolk-granules, makes its 

 appearance in the half of the egg opposite the polar globule. This sub- 

 sequently takes a position in the centre of the e^^, its radial system 

 having become more extended. After the second polar globule is formed, 

 this system becomes less distinct, and when the vacuoles make their 

 appearance in the semi-spindle lying under the polar globules, there 

 also appears at the centre of this central area a small vacuole. The 

 peripheral vacuoles unite into one, and then both peripheral and central 

 vacuoles, by the appropriation of nuclear fluid, become swollen to vesi- 



