36 ART. 17. — N. YATSU. 



larva is formed even after the cleavage pattern has been altered 

 by pressure in the sea-urchin egg and even in such a highly 

 specialized egg as that of Nereis. In these cases the nuclear 

 arrangement is changed but the plasma organization may be 

 unaltered. But in Driescii's shifting experiment ('96, '02) and 

 mine by means of Ca-free sea-water (Fig. 25 a, A) (cf. Sutton's 

 observation described by Wilson 'Oo p. 428) actual disarrange- 

 ment of egg organization must have taken place. Nevertheless 

 the result was larvae which were not very abnormal. From this 

 fact one can hardly escape from the conclusion that there is a 

 factor which in some way brings back shifted blastomeres to the 

 normal position, or if not, to a location such that they may sub- 

 sequently be able to produce a larva deviating only a little from 

 the normal. The factor that is active in the closing up of open 

 blastulas is in all probability of the same nature. At any rate, 

 further study especially directed towards the elucidation of this 

 factor is very desirable in the present state of experimental 

 embryology. It may here be added that even after a consider- 

 able cytolisthesis during the restitution to the final stage, blas- 

 tomeres retain their original potencies as is shown in multiple 

 gastrulations {e. g., Fig. 25 C. D) and multiple apical organs {e.g., 

 Fig. 24 B. C. E). 



Zoological Institute, 



Imperial University, Tokyo. 

 May 27, 1910. 



