II. ONTOGENY 353 



A piece of this part, when transplanted onto another part of embryo, 

 is able not only to retain its specific structure but also to exert its 

 structural influence upon surrounding tissues until a new embryo is 

 formed around it. The ectoderm of the ventral and lateral surfaces 

 of the frog embryos normally develops into epidermis, while ectoderm 

 of the mid-dorsal region gives rise to the neural plate ; however, when 

 the dorsal lip of the blastopore, the portion called organizer, is trans- 

 planted beneath the ectoderm on the ventral or lateral regions of a 

 frog at the gastrula stage, the ectoderm Governing such a transplanted 

 dorsal lip gives rise to a neural plate, not to epidermis. 



Such an action of organizer to induce a nervous system is appar- 

 ently brought about by a hormone-like factor, which has proved to be 

 a steroid. It has been shown that a v^ariety of lipids induce experi- 

 mentally a similar effect, but it cannot be said that the physiologically 

 acting factor is entirely identical with the substances which may ex- 

 perimentally exhibit a similar action. 



In addition to this inducing action, the organizer like viruses is 

 capable of transmitting its structure to surrounding protoplasm. Thus, 

 a portion of embryo which has no inducing action in itself, if trans- 

 planted onto a region near the organizer, will be endowed with the 

 inducing action, becoming itself an organizer, indicating that the 

 structural pattern of the organizer is transferred to the transplanted 

 region. 



In short, the organizer having developed under a specific influence 

 of environment has a strong structure comparable to fixed viruses, and 

 can transmit its structure like viruses. In addition it can produce a 

 substance, a kind of hormones, which can induce peculiar "crystal 

 shape" in its surroundings. This hormone may assist the virus-like 

 action of the organizer, providing the specific structure to surrounding 

 cells ; as a consequence these latter cells may become the second or- 

 ganizer which in turn produces another hormone. Thus, differentiated, 

 strong structures may be successively induced. 



These successively induced organizers, however, may not be iden- 

 tical with the first organizer in their structure, even if they were 

 induced by virus-like agents, for each portion of embryo is under each 

 different environmental condition ; each portion adapts itself to each 

 environment to attain strong structure ; and if a stronger structure is 

 present near it, it will be influenced by the structure, but without be- 

 coming entirely identical with the stronger structure which may exert 

 its influence as a virus. According to their different structures, each 

 organizer may produce each different hormone-like substance, thus ex- 

 tremely complicated "crystal shape" being formed. 



Since the substances behaving as hormones, whether steroid or 



