228 CHARLES R. STOCKARD 



embryo. If this process (evidently meaning disintegration) is 

 sharply localized, for instance, in a portion of the spinal cord or 

 in the brain, spina bifida or anencephaly results. To produce 

 a striking result, as in cyclopia, a small portion of the brain must 

 be affected at the critical time." 



The one position with which we are entirely unable to agree is 

 that the arrested development must so constantly be "associated 

 with the destruction of tissue." This tissue destruction is not at 

 all essential to the production of such defects as spina bifida or 

 anencephaly. It may be demonstrated in many experimental 

 cases that the tissues fail entirely to arise or differentiate without 

 there being any indication whatever of a previous destruction. 



As stated in the beginning. Mall included localized anomalies 

 among his normal specimens, yet such anomahes occurred about 

 twice as frequently among the pathological individuals as among 

 the normal. This is closely in accord with what has been found 

 for the abnormal fish embryos. 



After this review of monstrous development in general, and 

 an analysis of its causes from the conditions found in the smaller 

 components of double individuals, we may consider in the fol- 

 lowing section the interaction, if such can be observed, among the 

 early organs in the single individual. It may be possible that 

 these organs are related to one another in their development in 

 somewhat the same manner as are the components of double 

 specimens. A further test, therefore, of the correctness of my 

 interpretations for abnormal development may be had in an 

 analysis of the relationships among the developing organs in the 

 single individual. 



8. THE DOUBLE INDIVIDUAL WITH UNEQUAL COMPONENTS AND 



AN ANALYSIS OF THE DEVELOPMENT OF ORGANS 



IN THE SINGLE INDIVIDUAL 



By way of introduction, we may further consider certain condi- 

 tions in developing plants on account of their apparent simplicity 

 and also their very striking suggestiveness in connection with an 

 analysis of the origin and growth of organs in the vertebrate 

 embryo. The imaginary elements involved in comparisons of 



