24 



ART. 17. — X. YATSTJ. 



to produce a pilidium witli only ono liippet. In one case a very 

 small fragment survived and gave lise to an invaginated larva 

 with an apical organ (Fig. 22. a. A). In still another case a 



Fig. 21. 



A, B and C, three larvœ produced by the section indicated by the 

 accompanying diagrams a, b and c respectively. 



gastrula was split lengthwise at the lower half, so that the two 

 pieces were connected together with a narrow bridge near the 

 animal pole. In the course of development the lower portions 

 came together and completely fused, producing in the end a 

 normal pilidium. In the fact that an operation like this, drastic 

 it may seem, does not do any harm to the resulting embryos, we 

 have quite a good reason for believing that the defects produced 

 by the other sections thus far mentioned are not due to their 

 weakening effect but to the actual deprivation of necessary 

 "formative stuff" or some other disturbances in the morphogenic 

 processes. 



B. Operations performed upon late gastrulas and young 

 pilidia. 



