Centrosome in Enucleated Egg-Fragments. 2()l 



III. EXPERIMENTS ON THE EGG AT THE METAPHASE OF THE 

 FIRST MATURATION MITOSIS. 



A. Enucleated Fragments Treated %vtth the CaCL Solution 

 Heat-Sterilization. 



a. Methods. The eggs were released in the sterihzed sea- 

 water, the precautions already stated being taken. Alter an houi 

 and half the operation was begun. Had the eggs been fertilized 

 they would have reached the two or four-cell stage by that time. 

 As a matter of fact, none went beyond the metaphase of the first 

 maturation mitosis. The eggs were cut singly into two with a 

 lancet known as Jaeger's straight keratomv knife. Both the 

 nucleated fragment {i. e., the one containing the mitotic figure) 

 and enucleated one were put for five minutes in separate dishes 

 with the sterilized sea-water so as to give them time to round up, 

 since sudden contact of fresh cut surface with a salt solution seemed 

 injurious. The enucleated fragments were examined and drawn. 

 Then they were transferred into the solution of CaCU prepared 

 with the sterilized sea-water. (See p. 290.) In it they were kept 

 for an hour or sometimes a little longer. (This length of time 

 was found to be the right one from the experiments made on the 

 entire eggs.) The enucleated fragments thus treated were then 

 put back into the sterilized sea-water. The water was changed 

 once. After from five to ten minutes the fragments were studied 

 in a compressorium, but not compressed. Some of the fragments 

 subjected to the above treatment were fixed with acetic sublimate 

 (saturated solution of sublimate 98 parts plus glacial acetic acid 

 2 parts). When they reached 90 per cent alcohol they were 

 stained with erythrosin and, after clearing, they were fastened on 

 a piece of ulva by means of celloidin-clove-oil. The iron-alum- 

 haematoxylin method was used for all sections. While the 

 enucleated fragments were in the CaCl. solution, the nucleated 

 ones were stained with aceto-carmine to see that the two ends of 

 the first maturation spindle were not injured by the operation. 



b. Cytasters Studied in Life. First I shall take up one particu- 

 lar case of the formation of cytasters as an example. The egg was 

 cut in a plane a little below the equator. In the animal half one 

 could see a dumbbell-shaped clear area, indicating the first matura- 

 tion figure (Fig. I a), while in the vegetative half not a single clear 

 spot was present (Fig. ic). The animal half was stained with 



