283 



Nachdruck verboten. 



On Regeneration and Transplantation of the Balancers of 

 Embryos of Diemyctylus (with a Note on the external Grills). 



By E. T. Bell, M. D. 

 (From the Anatomical Laboratory of the University of Missouri.) 



With 9 Figures. 



DuriDg March 1907 a number of experiments were made on 

 embryos of Diemyctylus viridescens to study the development and the 

 regenerative powers of the balancers. 



The balancer may be regarded as an ectodermal tube whose 

 cavity is occupied by mesoderm. Inasmuch as it consists of both 

 ectodermic and mesodermic tissue, one thinks of three relations one 

 of which must exist between these tissues during development. 1) The 

 ectoderm exercises the controlling influence during development, the 

 mesoderm playing a passive role. The formative substance is located 

 in the ectoderm. According to this conception one would expect that 

 the ectoderm of the balancer-forming region can cause any undifferen- 

 tiated mesoderm to form the core of the balancer. This theory may be 

 tested by transplanting the ectoderm to some other part of the body. 

 2) The mesoderm exercises the controlling influence, the ectoderm 

 playing a passive role. In accordance with this conception one would 

 expect that the mesoderm of the balancer-forming region can cause 

 any undifferentiated ectoderm to form the ectodermal part of the 

 balancer. This theory is difficult to test directly. If it be possible 

 to replace the ectoderm of the balancer-forming region with ectoderm 

 from some other part of the body, a satisfactory result may be ex- 

 pected. I have not succeeded with this operation. 3) A third possi- 

 bility is that the ectoderm and the mesoderm of the balancer-forming 

 region develop parallel, neither controlhng the development of the 

 other. Both tissues are necessary for the formation on the balancer, 

 and neither can form the complete organ without the other. This 

 theory may be tested by transplanting the ectoderm of the balancer- 

 forming region. • 



