288 Naohide Tatsu. 



Ihis method ot examining the problem was first employed by 

 Wilson in 1901 by shaking to pieces the unfertilized eggs of 

 Toxopneustes and treating the enucleated fragments thus obtained 

 with iVIgCU solution. He found, upon studying the living frag- 

 ments, that not only do asters appear in such fragments, but also 

 that some of them have the power of division like the normal 

 asters. In sections he observed that the asters thus formed con- 

 tain in some cases the centriole. He, therefore, drew the con- 

 clusion that these centrioles must have been formed de novo. 

 Subsequently Meves and Wassilielf almost simultaneously raised 

 objections against Wilson's method and cast doubt upon his 

 results on a priori ground. Meves thinks that by shaking the 

 egg center may be thrown out into the cytoplasm, while Wassilielf 

 takes the view that shaking may bring about the flowing out of 

 the nuclear fluid from the egg-nucleus. To meet these criticisms 

 Professor Wilson suggested to me in February, 1903, to carry out 

 similar experiments on enucleated fragments obtained by cutting 

 eggs individually. In the summer of 1903 I made series of experi- 

 ments at the Harpswell Laboratory on the eggs of Cerebratulus 

 lacteus and obtained clear evidence that cytasters do appear in such 

 fragments, provided the egg be cut after the first maturation figure 

 is formed (which in this egg occurs before fertilization) ; no cytasters 

 are found, however, if the operation be performed before the 

 germinal vesicle has faded. I tried similar experiments on the 

 egg of Echinarachnius parma and found that here cytasters arise 

 in enucleated fragments from the matured egg. In the meantime 

 Petrunkevitsch independently attacked the same problem in 

 enucleated fragments obtained both by shaking and by cutting 

 the eggs singly. In none of the fragments did he find asters 

 containing a centrosome. He was, therefore, led to the con- 

 clusion that in the whole eggs the centrosomes in the cytasters 

 are the division products of the egg center. The obvious inade- 

 quacy of his evidence has been pointed out by Wilson in a brief 

 rejoinder ('04).^ 



In 1904 I undertook a repetition and extension of the experi- 

 ments of the previous year during my stay at the Harpswell 

 Laboratory, confining my attention to the egg of Cerebratulus 

 lacteus. Fortunately I obtained very consistent and constant 



'A more detailed historical review of literature I shall take up later on (see p. 304, et seq.) 



i 



