MICRODISSECTION STUDIES. 325 



time and then swells. The changes appreciable to the eye are 

 shown in Fig. 7. During the swelling of the nucleus a substance 

 apparently separates out which collects into a small mass and 

 persists as a gelatinous body. It is possible that this abnormal 

 separating out is analogous to the formation of the definitive egg 

 nucleus in the normal process of maturation. This separating out 

 of a gelatinous material from a liquid nucleus upon injury may be 

 similar to the method of precociously inducing chromosomes in 

 spermatocytes of the grasshopper (Chambers, '14). 



2. THE EXISTENCE OF AN EXTRANEOUS MEMBRANE ABOUT THE 



UNFERTILIZED EGG. 



The existence of a membrane about the unfertilized egg rising 

 off as the fertilization membrane upon insemination was first sug- 

 gested by the earlier investigators (e.g., Hertwig, '76; Herbst, 

 '93). Kite ('12) and Glaser ('13) agreed with them whereas 

 McClendon ('14), Harvey ('14) and Elder ('13) claimed that the 

 fertilization membrane is a new formation consequent to fertiliza- 

 tion. Heilbrunn ('13) also identifies it with the actual proto- 

 plasmic surface of the egg, which he considers to be in a state 

 of a gel and which lifts off as the fertilization membrane, a new 

 surface film forming over the egg underneath it. 



My experiments indicate that the unfertilized eggs of the 

 starfish, sea-urchin and sand-dollar all possess a membrane ex- 

 traneous to their true protoplasmic surface, and that it is this 

 membrane which, upon insemination, is lifted off as the well-known 

 fertilization membrane. 



In the unfertilized egg the membrane is more or less tightly 

 glued to the surface of the egg just as Kite ('12) described it. In 

 the sea-urchin egg it is extremely delicate and can be demonstrated 

 only as follows (Fig. 8) : The needle is inserted as nearly as possi- 

 ble through the periphery of the egg and left there. Within a few 

 seconds the protoplasm, lying immediately under the egg mem- 

 brane and distal to the needle, flow away from the needle until 

 the needle lies in a small protuberance which is formed by a 

 very slightly lifted portion of the egg membrane. 



The existence of the egg membrane is easily demonstrated in the 



