188 G. E. COGHILL 



II. THE PHYSIOLOGICAL PART 



In the treatment of the physiological part of this paper it is 

 necessary, first of all, to show that the results of the various ex- 

 periments which are to be discussed have to do with the afferent 

 system of the trunk as opposed to that of the head, since the 

 scope of this paper is explicitly limited to the problems of the 

 sensory system of the trunk. 



As already noted in the anatomical part, the definitive spinal 

 nerves have no place in this problem since there are no dorsal 

 spinal roots during the period under investigation. There is, 

 however, more or less overlapping of the sensory field of the giant 

 ganglion cells by the lateral line nerve and possibly by the cutan- 

 eous component of the vagus, and this community of area in 

 distribution of the nerves from the two regions requires particu- 

 lar analysis. The anatomical details of this relation are left 

 for a later consideration of the cranial system of nerves; but the 

 distribution of the lateral line primordia has been given in the 

 anatomical part of this paper, and the distribution of the general 

 cutaneous component of the vagus has been described in my 

 earlier studies on the cranial nerves of larval Amblystoma ('02). 



Upon the basis of anatomical facts from these sources, one is 

 able, by the simple experiment of transecting an embryo at about 

 the level of the second myotome, to convince himself that the 

 cranial nerves mentioned do not play any distinctive part in the 

 reactions to stimulation upon the trunk, for the trunk of an em- 

 bryo that has been transected in the manner indicated exhibits all 

 the peculiarities of irritability that characterize the normal embryo. 

 Indeed, there is not in all my experimental work upon the subject 

 any evidence that the lateral line system during this period of de- 

 velopment influences behavior in any way, or that there is any 

 difference between the cranial nerves and giant ganglion cells as 

 regards cutaneous irritability. There is no occasion, therefore, to 

 question the validity of the experimental evidence to be presented 

 in this paper concerning the receptive functions of the giant 

 ganglion cells as the afferent system of the trunk. 



