THE NERVOUS SYSTEM OF AMPHIBIA 297 



portion of the medulla oblongata must be capable of conducting 

 stimuli for a considerable period before they can be excited by 

 normal stimulation of the retina. The development of the olfac- 

 tory nerve and centers suggests that the same principle applies 

 to much of the central nervous system in early development. 

 We have, then, within our knowledge of the development of 

 reflexes and reflex arcs no rational basis for cytological studies of 

 the difi"erentiation of the neurone as correlated with the develop- 

 ment of nervous function. It is hoped that the studies which 

 are now in progress upon the central conduction paths will furnish 

 such a basis for cytological investigations; and that the api)li- 

 cation of cytological methods to nerve cells of known physio- 

 logical capacity may reveal the essential structural basis of con- 

 duction in the neurone. 



5. The cranial nerves of Amphibia 



Some points of interest concerning the morphology and devel- 

 opment of the cranial nerves of Amphibia deserve mention here. 



In my paper on the cranial nerves of Amblystoma ('02, p. 215, 

 and figure 1) the lateralis ganglion which corresponds to Vila 

 of this paper is described as closely fused with the ganglion of the 

 ophthalmicus profundus, and the latter as very intimately related 

 with the Gasserian ganglion. In the younger embryos of this 

 study these ganglia are widely separated, but in the latter part 

 of the period under in\Tstigation these ganglia, particularly the 

 Gasserian and profundus, approach each other rapidly, and 

 finally the Gasserian and profundus ganglia estabhsh a wide 

 contact, the lateralis ganglion VII a stiU standing apart from 

 them. A similar change, though of less degree, occurs in these 

 ganglia in Rana pipiens, according to Landacre and McClellan 

 ('12), who describe the ganglion of the ophthalmicus profundus 

 in the 8 mm. embryo as standing out "rather distinctly, indi- 

 cating its definite character," and as being much more isolated 

 in younger stages. In the early development, therefore, of both 

 Anura and Urodela there is a process of consolidation going on 

 between the various ganglia of the V -|- VII complex, a process 



