376 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



EXPLANATION OF PLATE XVIL 



Fig. I. Scheme of 5"^'^«c»52f(?;;^a undergoing normal fission in the plane 



F. P. The several elements entering into the experimental 

 treatment of the animal are here shown. For the abbrevia- 

 tions pertaining to these see page 367. 



Figs. 2 to 2*. A parent worm (2) and its derivative at various stages in its 

 development, produced by the cut a. c. with the con- 

 sequent inhibition of F. P. 2* is the fully formed young 

 made up of P. Y. -\-a.f. p. and is beginning to develop 

 F. P. for the second generation. 



Figs. 3 to 3^ Another series similar to 2, though not going through to the 

 adult young. This series was selected as being a case in 

 which the migration of the ganglionic cell-masses (c. m.) 

 was particularly well shown. 



The following abbreviations in addition to those given in the text are used: 

 c. m.., ganglionic cell-mass. 

 c. p.., ciliated pits. 

 g., cerebral ganglia. 

 m., mouth. 

 ph., pharynx. 



