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ROBERT CHAMBERS. 



plete fertilization membrane formed around the egg except at 

 the two torn spots and cleavage followed. 



Endoplasmic exovates were also produced which remain con- 

 nected by a bridge of protoplasm to the collapsed cortical portion 



FIG. 25. a, nucleated exovate of internal cytoplasm produced by squashing 

 a starfish egg. b, fragments inseminated after the endoplasmic sphere was 

 pinched off. Only the ectoplasmic remnant forms a fertilization membrane. 

 c, the endoplasmic sphere remains inert and nonfertilizable (cf. Fig. 12). 



FIG. 26. a, starfish egg squashed producing two endoplasmic exovates. 

 b, the nucleated exovate was pinched off. Upon insemination the other ex- 

 ovate drew back into the ectoplasmic remnant which formed a fertilization 

 membrane. c, d and e, the ectoplasmic remnant underwent segmentation 

 showing that the disturbance due to the squashing does not prevent segmen- 

 tation. The endoplasmic sphere remains inert (d). 



of the egg. On being inseminated the exovate either is drawn back 

 into the cortical portion as the latter rounds up with the formation 

 of a fertilization membrane or is pinched off, after which it remains 

 as an inert body. 



The possibility suggested itself that the substance which renders 

 an egg fertilizable has a tendency to collect in the surface film of 

 an egg and that, if an exovate remained in organic continuity with 

 the egg, this substance might spread to the surface film of the 

 exovate, thus rendering it fertilizable. Endoplasmic exovates were, 

 therefore, produced which remained connected for varying lengths 

 of time with the cortical portion of the egg. Some of the exovates 

 remained connected for as long as fifteen minutes. Before insemi- 



