290 G. E. COGHILL 



nerve into the ininiediate vicinity of the motor centers in the 

 lower portion of the medulla oblongata. 



c. Such irregularity as appears early in development in the 

 direction of movement relative to the side touched depends upon 

 the condition that the point of adequate stimulus is not the point 

 actually touched, by reason of the variability in the threshold 

 of stimulation of reflex arcs as a whole, and not upon diffuse 

 conduction through the nervous system. Reflex arcs are from the 

 first definite and fixed during the period under consideration. 



d. The afferent system of the head is like that of the trunk 

 with reference to chemical stimulation. 



e. A slight responsiveness to high illumination of the retina 

 occurs about the time the animal begins to swim, and this is in 

 close correlation with the development of the first fibers of the 

 optic nerve into the brain. Owing to the exceedingly embryonic 

 condition of the retina at this time this topic demands further 

 investigation. 



f. Although the olfactory nerve is well established at the end 

 of the period under investigation there are no perceptible reac- 

 tions to olfactory stimulation. 



g. There is no available evidence that the auditory organ or 

 lateral line nerves have any part in reactions, although the latter, 

 judged upon the basis of its anatomical relations, would be re- 

 garded as more efficient than the ganglionic general cutaneous 

 system. 



h. The physiology of the eye, olfactory organ, auditory organ 

 and lateral line organs require further investigation in connec- 

 tion with anatomical studies of the brain, which are now in 

 progress. 



III. DISCUSSION 



It is the purpose to deal here with the work of other investi- 

 gators which seems to have direct bearing upon the results of 

 this paper. 



