MICRODISSECTION STUDIES. 



331 



the fertilization membrane was formed, showing its continuity 

 with the delicate membrane previously noticeable (Fig. 15-^)- 



FIG. 14. Sea-urchin 'egg with surface torn producing local cytolysis. a, a 

 new surface film has formed under the cytolyzed area which is. being ex- 

 truded, b, a bulge appears in the region of the new surface showing this 

 region to be weaker than elsewhere on the egg surface, c, egg after fertiliza- 

 tion exhibiting a fertilization membrane over the egg except at the place 

 previously torn, d, the same egg 35 minutes later with a blastomere pro- 

 truding through the tear. 



FIG. 15. a, needle piercing sea-urchin egg near its periphery. The cyto- 

 plasmic granules are flowing in the direction of the arrows. One minute 

 later the egg was inseminated, c, an intact fertilization membrane forms, 

 inclosing both egg and needle tip. 



FIG. 1 6. a, protrusion on surface of egg produced by pulling at cortex 

 with needle, b, three minutes later the investing membrane lifted off surface 

 of protrusion, c. one minute after fertilization. The protrusion has been 

 pinched off from the egg and its investing membrane can be seen to be con- 

 tinuous with the fertilization membrane, d, empty and collapsed fertiliza- 

 tion membrane. 



In the sea-urchin egg the membrane often rises off a protrusion 

 caused by pulling at the cortex with the needle. Such a case 

 is shown in Fig. 16. The protrusion was formed at 12:43. At 

 12:46 a membrane had lifted off the protrusion. At 12:51 the 

 egg was inseminated, and one minute later the membrane was 



