262 CHAKLES R. STOCKARD 



are the most frequent causes of embryonic death as well as mon- 

 strous development. The existence of the species may frequently 

 depend upon some means of regulating the developmental envi- 

 ronment. Species may be lost during evolution not only on ac- 

 count of failure of their adult structures to fit them for existence, 

 but equally as a result of failure to obtain an environment in 

 which their embryonic development is possible. The highly com- 

 plex forms, such as birds and mammals, with a long embryonic 

 period have partially succeeded in controlling their develop- 

 mental environment. But in no case is the regulation constantly 

 perfect and this fact is the underlying cause of frequent malfor- 

 mations and monstrous productions. 



17. The double fish specimens with unequal components and 

 the growth reactions between these components are important 

 in connection with certain teratomal conditions in man. If 

 teratoma in man frequently originates as a twin inclusion, we 

 may expect an antagonistic growth reaction to exist between the 

 teratoma and the host. While the host individual is rapidly 

 growing the teratoma will be suppressed and when the host 

 slows its growth the teratoma should tend to grow more rapidly. 

 There should thus be a correlation between the postnatal growth 

 curve and the time of enlargement or recognition of teratomata. 

 Dr. H. E. Himwich has undertaken a survey of this subject which 

 will soon be published. 



18. The interaction between the growing organs of a develop- 

 ing individual has been discussed in its relation to regeneration 

 and cancerous growths of old age. In the old individual with but 

 little normal growth still present there can be but slight inhibi- 

 tion to any regenerative process that may be set up following a 

 continued trauma. • 



