Centrosome in Enucleated Egg-Fragments. 299 



d. Nature of the Central Granule and Development of the 

 Cytaster. It is highly important to determine whether the dark 

 jjranules tound in the cvtaster of the enucleated fragments now 

 under consideration are real centrioles or not. The direct com- 

 parison of these cytasters with the asters of the normal egg is, 

 I think, not just for the reason that, even if the normal aster did 

 appear in the enucleated fragment, it would have been acted 

 at the same time by the salt solution. The more reasonable 

 way, it seems to me, would be to compare our cytasters with the 

 asters found in the entire CaClj eggs. 



Fig. 10 shows a portion from a section of an entire egg shaken 

 fifteen times, treated for an hour with the CaCL solution and 

 fixed after ten minutes' sojourn in sea-water.^ 



In the section one observes a large centrosome at either end 

 of the first maturation-spindle; single at the right, and double 

 at the left — the latter undoubtedly a division-product of one 

 original centrosome, as shown by the course of the spindle fibers. 

 Besides these, four asters are found in the vicinity. Noteworthy 

 is the abnormal growth of the centrosome and extraordinarily 

 rapid multiplication of the centrioles in the centrosomes. (cf. 

 Wilson, '01, Figs. 24, 25 and 34.) 



Another section shown in Fig. 1 1 illustrates these points very 

 clearly. This is from an egg shaken fifteen times, treated with 

 the CaCl, solution for an hour and killed after five minutes' 

 sojourn in sea-water. Only the central aster of the first matura- 

 tion mitosis is pictured here. (cf. Morgan, '99, PI. 10, Fig. 67.) 

 The centroplasm of colossal size is surrounded by irregular rays, 

 and in it one sees a number of dark stained granules. That 

 these granules are really the centrioles can clearly be demonstrated 

 in Morgan's figures (PI. 10, Figs. 68, 70 and 60B), each granule 

 having acquired a new ray system about it. 



From the above two examples it will be seen that CaCL has 

 *the power to call forth two independent phenomena at the same 



'This lot of eggs was originally intended for the study of cytasters in enucleated fragments obtained 

 by shaking, but quite a number of eggs escaped from being broken. It is noteworthy that shaking has 

 no effect at all on the mitotic figure, nor are the cytasters produced by it. We may, therefore, safely 

 look upon all the changes that have taken place in the section about to be described, as due to the action 

 of the CaClo solution. Although it may be claimed that these changes are caused by the combined 

 action of shaking and CaCl2, yet I think the comparison does not lose its validity for our present purpose, 

 since the operation of cutting might give the egg as strong a shock as shaking does. 



