IS THE CONTROL OF EMBRYONIC DEVELOPMENT 

 A PRACTICAL PROBLEM? 



By CHARLES R. STOCKARD. 

 (Read April iq, igi2.) 



Under favorable natural conditions two normal parents should, 

 and usually do, produce a vigorous normal offspring. When, how- 

 ever, the conditions of development are modified or if in the second 

 place the parents are not entirely normal the offspring is usually 

 more or less defective. I shall attempt to show that the proper 

 development of the offspring is dependent upon two main factors, 

 first the physical qualities of the parental germ cells, and second the 

 environment in which the embryo develops. 



One is at first sight apt to think that deformities and defects 

 are rare among men and other animals ; but closer observation will 

 show that the really structurally perfect individual is rather excep- 

 tional. Gross anatomical defects or monstrosities are frequently 

 found among all animals, while lesser defects of minor importance 

 are to be observed in a majority of individuals. These defects often 

 cause no inconvenience, and indeed, we may be ignorant of their 

 presence, since they are generally internal. Yet many apparently 

 normal individuals sooner or later suffer or may actually die from 

 some hidden developmental imperfection. The well-known con- 

 genital defects of the heart and other parts of the vascular system, 

 digestive tract, etc., as well as the numerous developmental arrests 

 in various parts of the body constantly remind the observer of the 

 great loss in ability and energy that the race suffers as a result of 

 faulty development. 



These defects in construction must be considered a disease which 

 causes the death of about 23 per cent, of the human race before or 

 shortly after the time of birth (Sullivan's studies and French sta- 

 tistics), and handicaps a certain proportion of the survivors through- 



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