Centrosome tn Enucleated Egg-Fragments. 305 



1. Asters and pseudasters {i. e.., asters without the centriole) 

 are produced de novo in the cytoplasm by the action of some salts. ^ 

 The presence or absence of the centriole in the aster is not due to 

 the action of fixing fluid ('00, p. 522). The centriole in the 

 cytaster is sometimes single, sometimes a group of granules ('96, 



P- 343)- 



2. The first step to the cytaster formation is a local accumula- 

 tion of hyaloplasm, rays are formed in it, and then the centrioles 

 develop at the center ('99, pp. 477 and 513). 



3. The cytasters become more distinct when the nuclear mem- 

 brane fades, while they become less marked when the nuclei 

 come into the resting stage ('99, pp. 468, 469 and 517). 



4. In the unfertilized egg cytasters develop more slowly and 

 are less distinct than those in the fertilized egg ('96, p. 344; 



'99' P- 473)- 



5. No cytasters appear before the dissolution of the germinal 



vesicle in the egg of Sphaerechinus ('96, pp. 348 and 349), and in 

 Sipunculus ('99, p. 502). 



In his paper on the nature of the centrosome Boveri ('01) 

 touches on the question of the cytaster in several places, although 

 he has no observations of his own. He distinguishes two kinds 

 of cytasters: one assumed to be descendants of the ovocenter, 

 and the other artificial asters (p. 169). Central bodies may be 

 present in the latter, yet their identification as centrioles is doubt- 

 ful, unless their division is actually observed. In other words, 

 he does not accept the formation de novo of the centrosome and 

 seems to incline to the conclusion that every centrosome in the 

 egg is a division product of the ovocenter.- 



In eggs of Toxopneustes treated with solutions of MgClj Wilson 

 ('01) confirmed the formation de novo of the centriole from the 

 study of sections as well as living eggs. Moreover, he, for the 

 first time, proved the above fact experimentally in enucleated 

 fragments. His results are as follows: 



* It is perhaps worth pointing out that R. Hertwig ('02) misquotes Morgan's experiment, stating 

 that he obtained cytasters in enucleated egg-fragments (p. 19). This is an error, the experiment 

 having been done for the first time by Wilson ('01). Fischer and Ostwald ('05) cite Morgan's 

 merogony experiment as giving the same result (p. 253), but this is also erroneous and in the papers 

 they referred to no experiment giving this result is described. 



^After the appearance of Wilson's paper ('01), Boveri accepted the formation de novo of the centro- 

 some ('02, p. 40). 



