1 A-RT. 17. — N. YATSÜ. 



More detailed results regarding the gradual progress of the 

 germinal localization were obtained in the experiments, which I 

 am going to describe in the present paper, than in those embodied 

 in previous papers. First of all the action of the spermatozoon 

 upon the establishment of a more definite egg-organization is to 

 be emphasized, as may be seen by comparing the conditions of 

 the ^%g before and after fertilization. It is also noteworthy that, 

 during the first cleavage and the 2-cell stage, neither vertical nor 

 oblique section has much effect on subsequent embryogeny, and 

 the horizontal cut, provided the removed portion be not large, 

 is not likely to produce defective larvae, whether performed on 

 one or two blastomeres. If the egg is cut along the equator, a 

 pilidium with a small enteron or entirely devoid of one results. 

 But section near the animal pole may produce at this stage a 

 larva with a defective gut instead of an anenterion. At the 

 4-cell stage bilaterality of the egg-organization has not yet been 

 established. At the 8-cell stage, as 1ms been shown by Zeleny, 

 the ectodermal and entodermal stuffs are dissociated from each 

 other, though in some cases the separation is not so sharply 

 defined as in his case. If the apical organ be cut off from the 

 pilidium, it is regenerated in the great majority of cases. If 

 the blastomeres be disarranged by either pressure or Ca-free sea- 

 water, the resulting larvœ are nevertheless pilidia in all their 

 characteristics, showing that there exists in the embryo not a 

 little power of bringing abnormal features back towards the 

 normal. If the egg be kept in Ca-free sea-water, a solid cell 

 mass results, hardly any differentiation taking place among the 

 blastomeres. Here fusion is often met with between neighboring 

 eggs. Yet the moment such cell-masses are transferred into 

 ordinary sea-water, the blastomeres begin to differentiate into the 



