Ceiitrosome in Enucleated Egg-Fragments. 293 



the cytoplasm no visible change took place while in the salt solu- 

 tion, nor could even the primary radiation be seen. After an 

 hour it was put back into the sterilized sea-water, afterward the 

 water was changed. The fragment became perfectly spherical 

 (Fig. le), but there was no visible indication of the cytaster forma- 

 tion. After about ten minutes a clear spot with rays around it 

 appeared near the center of the fragment. (Fig. if.) This cen- 

 tral area grew very rapidly, reaching after half an hour almost the 

 size of the germinal vesicle. It ceased to enlarge at this stage. 

 During the growing period the rays became indistinct, so that 

 the clear area gave the appearance of a vesicle. It should here 

 be noted that the size of the fragment did not change perceptibly 

 during the formation of the clear area. {ef. Fig. le and if.) 



The above case with a large spherical central area is the com- 

 monest mode of appearance of the cytasters, while quite often 

 the clear area has an irregular outline or a deep indentation on one 

 side. Fig. 2a shows an enucleated fragment, in which, under 

 the same treatment, appeared two clear areas with fine radiation. 

 These two made their appearance simultaneously at two separate 

 spots. They, therefore, are not the division product of one 

 original aster. The stained nucleated half from the same egg 

 IS represented in Fig. 2b. In one enucleated fragment three 

 clear spaces of about the same size appeared, as is shown in Fig. 3. 

 In another three areas of different shape were found. (Fig. 4.) 

 In still another case a splendid display of the cytasters was seen 

 (Fig. 5a), ^ dozens of small asters being scattered throughout 

 the fragment; the enucleated half of this egg is drawn in Fig. 5b. 



c. Cytasters Studied in Sections. Nine enucleated fragments 

 subjected to the CaCL treatment w^ere fixed after from twenty to 

 thirty minutes' sojourn in the sterilized sea-water and cut into 

 sections. One of them had no asters in it; the mode of appear- 

 ance of the cytasters studied in the remaining eight fragments 

 may conveniently be classified in three categories: a, the cytas- 

 ters found throughout the cytoplasm; b, one single large aster at 

 the center of the fragment, and c, a group of cytasters in a large 

 central clear area. 



a. In four fragments several cytasters made thier appearance 



'This fragment has been drawn greatly compressed. Some twenty asters are left out in this figure 

 owing to the difficulty of drawing all of them in perspective. 



