FERTILIZATION REACTION IN ECHINODERM EGGS. 263 



the elevation of the vitelline membrane as the fertilization 

 membrane. Such evidence is not entirely satisfactory for the 

 echinoderm egg as the vitelline membrane is not clearly visible 

 on such eggs. Chambers' evidence appears to be conclusive. 

 He has shown that if the vitelline membrane be removed from 

 unfertilized eggs (Arbacia, Asterias, Echinarachnius}, such eggs 

 do not elevate membranes on fertilization. Further by various 

 methods the vitelline membrane can be made more obvious on 

 the unfertilized eggs at certain points and the continuity of these 

 easily visible portions of the membrane with the fertilization 

 membrane after insemination is easily observable. 



Further conclusive evidence of the identity of the vitelline 

 and fertilization membrane is afforded by the study of the fer- 

 tilization reaction in egg fragments. That portions of eggs may 

 elevate fertilization membranes has been noted by Ziegler ('98), 

 Moore ('12) and Glaser ('13). The fragments in these experi- 

 ments were obtained by shaking the eggs and hence it is not 

 known from which portions of the eggs they originate. It is 

 certainly not justifiable to conclude from such experiments that 

 any portion of the egg when isolated can reform a membrane 

 capable of elevation since: (a) the cytoplasm being relatively 

 fluid, much of it will be lost on rupture of the eggs and the cortical 

 portion which adheres to the membrane will be most likely to 

 persist; and (b) since it has been proved by Chambers ('210, J 2ib) 

 and Just ('23) that the interior of the egg is not fertilizable but 

 only the cortex possesses this property, it follows that any frag- 

 ments which fertilize must necessarily have retained a portion of 

 the egg cortex and hence of the original vitelline membrane. It 

 seems likely that most of the egg fragments obtained by shaking 

 represent the whole cortex, the fluid interior having escaped. 



I have studied the fertilization reaction in fragments of the 

 eggs of all three species used. These fragments have-been obtain- 

 ed by the method already described. An egg is held by surface 

 tension and then punctured. The cytoplasm flows out and the 

 egg begins to disintegrate. At various stages in this process the 

 egg is rapidly pushed back into the interior of the drop. The 

 outflow at once ceases when the pressure of surface tension is 

 removed and portions of eggs of all sizes and shapes are obtaina- 

 ble. Such fragments of course always retain a portion of the 

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