MICRODISSECTION STUDIES. 341 



rendered possible by the microdissection instrument it has been 

 possible to work out this problem in detail and to ascertain to 

 some extent the distribution of the material which renders fer- 

 tilization possible. 



A number of fully grown immature starfish eggs were enucleated 

 by carefully dissecting out their germinal vesicles. None became 

 fertilized when inseminated. In another lot of immature eggs the 

 germinal vesicle was torn while in the egg (Fig. 21). Immediate 



FIG. 21. A starfish egg whose germinal vesicle is eliminated by puncturing 

 it (cf. Fig. 9). The cytoplasm surrounding this nucleus was also destroyed. 

 This enucleated remnant is nonfertilizable. 



dissolution of the nuclear membrane took place with a disintegra- 

 tion of the cytoplasm around the nuclear area. Those eggs which 

 succeeded in forming a protective surface film to prevent spread 

 of the disintegration process subsequently rounded up. Upon in- 

 semination none of the eggs showed any sign of being fertilized. 

 Eggs were then taken with the germinal vesicle in various stages 

 of normal dissolution and cut into nucleated and non-nucleated 

 portions. The eggs may be grouped into stages b, c and d, accord- 

 ing to the stage of dissolution of their germinal vesicles, as shown 

 in Fig. 6 (page 323). Whenever the cut passed through the nu- 

 clear area during the nuclear stages b, c and d, disintegration al- 

 ways took place, involving all of the nucleated portion and a small 

 part of the non-nucleated piece (Fig. 23 a, b and c}. When the 

 cut did not pass through the nuclear area all persisting nucleated 

 portions matured normally and upon insemination formed fer- 

 tilization membranes and segmented. Of the non-nucleated por- 

 tions those from eggs in stage b are non-fertilizable (Fig. 22). 

 Those from eggs in stage c form fertilization membranes upon 

 insemination. Nuclear division also takes place, so that the egg 



