466 C. M. Child. 



genital ducts are indicated only by the "genital area" posterior 

 to the pharynx as this was all that could be distinguished with 

 certainty except when the ducts were filled with sexual products. 



B. GENERAL CONSIDERATIONS REGARDING THE RELATION 



BETWEEN THE CENTRAL NERVOUS SYSTEM AND 



MORPHOGENESIS. 



The existence of a relation between the nervous system and both 

 morphogenesis and the maintenance of form has been established 

 or regarded as probable in various cases, some of which have 

 already been mentioned. Some authors postulate the existence 

 of special nervous "formative stimuli" and "trophic" nervous 

 stimuli have been much discussed. But the relation between the 

 nervous system and morphogenesis is of a problematic character, 

 though the existence of a relation of some sort can scarcely be 

 denied in many cases. 



This relation may conceivably be either direct or indirect. In 

 the first case particular nervous stimuli of some sort are to be 

 regarded as constituting in themselves formative factors. In the 

 second case in consequence of certain nervous stimuli a particular 

 part may be subjected to certain conditions which may be the 

 formative factors, though themselves wholly different in character 

 from nervous stimuli. The conditions connected with and 

 resulting from a particular functional activity of a motor organ 

 constitute a good example of the indirect relation. In general the 

 functional activity of a motor organ is determined and controlled 

 more or less completely by the nervous stimuli which affect it and 

 adjoining regions. In consequence of these stimuli it functions 

 more or less perfectly in a particular manner. The functional 

 activity subjects the tissues of the part to a great variety of con- 

 ditions, physical and chemical, external and internal, which, 

 however, considered as a whole constitute a characteristic com- 

 plex. Change in the kind or degree of functional activity is of 

 course accompanied by changes in the complex of functional con- 

 ditions to which the part is subjected. If these conditions play any 

 part in the morphogenesis or form-maintenance a relation between 

 the nervous system and form will appear to exist in such a case, but 



