GERMINAL LOCALIZATION IN THE EGG OF CEREBRATULUS. 23 



Series S. Isolation Experiment at the 8-cell 

 Stage by Vertical Cut. 



An egg of the 8-cell stage was cut in two vertically, each 

 part consisting of 2 A and 2 V. Four pilidia were produced 

 from such fragments, and all were perfect, no sign of asymmetry 

 being detected. 



I had another group of 2 A and 1 V. This also gave rise 

 to a perfect pilidium. 



Series T. Removal Experiment performed upon 

 the Blastulas and Gastrulas. 



A portion of the blastula, early and late gastrula was cut 

 off and the fragments were reared.' Thirty two pilidia were 

 obtained. The result may conveniently be described under two 

 headings. 



A. Operations performed on blastulas and young gastrulas. 



a. Horizontal Sections — Only three larvse were successfully 

 reared up to the pilidium stage, tw^o animal larvae (Fig. 21 a, A, 

 b, B) and one vegetal one (Fig. 21 c, C). One of the animal 

 larvie had a small gut and the other none at all. It is interest- 

 ing to observe that the vegetal larva too was provided with an 

 apical organ. 



b. Vertical or oblique sections — Seventeen pilidia were 

 derived from the operations. This series of experiments afforded 

 no data worth mentioning, save the fact that vertical cuts are liable 



7 In passing it may be stated that tiny fragments of blastulas and gasturlas swim 

 about very rapidly and rarely continue to live through to the pilidiam stage, since they 

 are liable to burst into nothing the moment they come to the surface of the water. 



