20 ART. 17.— X. YATSÜ. 



tlie npical organ. From seven Inte gastrulas or yonng pilidia 

 the apical organ together with a considerable portion of the 

 animal region was cut off; of these three developed into pilidia 

 without the apical organ, while the rest regenerated the organ 

 (Fig. 22. b, B) though in one of them the tuft was abnormally 

 short (Fig. 22 e, C). 



In two cases the pilidia were split vertically in the oral 

 region. Contrary to the case just mentioned the tw^o separated 

 parts did not fuse together, but gave rise to barrel-shaped larvae 

 (Fig. 22 d, D, E). In one of them one notices the guts at both 

 the ends ; while in the other, the enteron appears as an open 

 tube with a diverticulum. 



Series U. Pressure Experiment. 



At the 2-cell stage the eggs were pressed gently under a 

 cover glass, and at the 16-cell stage the pressure was removed. 

 When the pressure was too strong the blastomeres divided ab- 

 normally, triasters or other atypical mitoses taking place. For 

 the present purpose, however, only those eggs which divided with 

 normal karyokinetic figures were allowed to develop into pilidia. 

 I had ten cases of this series. At variance with the results of 

 pressure experiments upon the egg of sea-urchin and Nereis the 

 resulting larvae were malformed in one respect or another. In 

 five the apical organ failed to develop (Fig. 23 a. A; b, B). It 

 is interesting to observe that, though in some double develop- 

 ment is apparent (Fig. 23 d, D ; e, E), yet as regards their 

 general make-up all of them comforms to that of the pilidium. 

 This shows clearly that the embryo has a tendency to be normal 



