STRUCTURE AND DEVELOPMENTAL RATE 251 



The ready manner in which the structures of the developing 

 individual are modified by changes in temperature and oxygen 

 supply makes it evident that the existence of the species often 

 depends upon some means of regulating the developmental en- 

 vironment. We may readily believe that species have been lost 

 during evolution not only on account of failure of their adult 

 structures to fit them for existence, but equally often as a result 

 of failure to obtain an environment in which their embryonic 

 development was possible. 



No developmental environment in nature is constantly per- 

 fect, and this fact is the underlying cause of the frequently occur- 

 ring malformations and monstrous productions. 



11. GROWTH COMPETITION BETWEEN THE TWO COMPONENTS IN 



DOUBLE INDIVIDUALS AND THE TIME OF OCCURRENCE 



OF TERATOMA IN MAN 



It has been clearly seen that in cases where one component of a 

 double individual is larger because of a more favorable location^ 

 the smaller has been inhibited in its growth and development by 

 the presence of the larger. In plants this inhibiting influence is 

 readily demonstrated, since on pinching away a growing shoot the 

 suppressed buds immediately spring into growth. There is much 

 evidence to indicate that a similar interaction exists between two 

 developing organs in a single individual. The alternating mo- 

 ments of rapid growth among the several organs of the embryo is 

 a case in point. 



With the preceding discussions of these propositions in view, 

 if it be now admitted that teratoma in man often originates as a 

 twin inclusion, we may expect an antagonistic growth reaction to 

 exist between the teratoma and the host. In other words, while 

 the host individual is rapidly growing, the teratoma will be sup- 

 pressed and when the rate of growth of the host individual be- 

 comes slow, the teratoma will tend to grow more rapidly. If 

 such an opinion be correct, there should be a marked correlation 

 between the postnatal growth curve and the time of enlargement 

 or recognition of teratomata. When the individual is growing 

 very rapidly during the first year and a half of infancy, few tera- 



