54 C. M. CHILD AND E. V. M. McKIE. 



In the development of the abnormal forms the eye undoubtedly 

 arises in connection with the central nervou^ system .1- it does 

 in the normal animals. The position and number of the eyes 

 must be determined primarily by the condition of the nervous 

 system, though other factors may play some part. Apparently 

 the median regions of the nervous system are more or less reduced 

 or fail to develop in the abnormal forms and the lateral region:- 

 consequently lie nearer together so that the eyes appear near 

 or in the median line. The approximation and fusion of the 

 auricles is also evidently due to the reduction or absence of the 

 median region of the head and this condition is undoubtedly 

 closely connected in one way or another with the condition of 

 the ganglia. There can be no doubt that the condition of the 

 nervous system is the most important factor in determining the 

 characteristic features of the teratophthalmic and teratomorphic 

 heads. 



One of the most interesting points in connection with the 

 whole series of forms is the fact that in the teratomorphic forms 

 the whole length of the regenerated nervous system is abnormal 

 (Figs. 13 and 14, Fig. 26, Fig. 30). Not until the level of the old 

 tissue is reached do the two cords appear in their usual relations 

 and even there they are commonly nearer together than in 

 normal animals (Figs. 15, 22, 27, 31). This fact suggests that the 

 development of the regenerated portion of the nervous system is 

 in large measure independent of the already existing portion. 1 1 

 the development took place in the anterior direction from the 

 cut ends of the nerve cords in the old tissue, it is difficult to 

 understand how such structures as those shown in Figs. 13 and 

 14, 26 and 30 could arise near the old tissue. Unt if the develop- 

 ment of the regenerated part takes place independently of the 

 old part, the continuation of the abnormal structure back to the 

 level of the preexisting portion constitutes a less difficult problem. 



According to recently published work of the senior author 

 (Child, 'ii</) the formation of a new whole from a headless pic i e 

 of Planaria consists essentially in the formation tirst of all ot a 

 new head region which then reorganizes the parts posterior to it 

 through correlation. The structure of the regenerated portion 

 of the nervous system in the teratomorphic lorms certainly oller> 



