336 JOURNAI. OF CoMPARATn'E NeUROI.OGY. 



spinal nerve with a slight ganglion, and observed its dorsal 

 branch approach the dorsal border of the myomere and its 

 ventral branch proceed on to uniformly small sympathic 

 ganglion. I do not know^ whether this myomere persists. 

 But in any case the pertaining spinal nerve would not be 

 reckoned among the cranial nerves. 



I have only succeeded in demonstrating three pairs of 

 dorsal and one pair of ventral spinal nerves of the head, and 

 that over an extent to which belong five pairs of epibranchial 

 ganglia. 



The spinal system is therefore in Ammocoetes, at least in 

 the stages of development known to me, of little value for 

 the determination of the segmentation of the head. The 

 epibranchial ganglia furnish the surest basis for this. 



I have enlarged so particularly on the cranial nerves of 

 Ammocoetes because, on the basis of what has been com- 

 municated, I am of the opinion that here very primitive rela- 

 tions exist, which furnish important hints for the criticism of 

 the cranial nerves of Gnathostomata. Three-fold phenomena 

 determine me to this view: First, the far-extending formation 

 of the epibranchial ganglia in the trigeminus region; then 

 the close proximity of the letis to this chain of ganglia^ 

 whereby a new light falls upon the phylogeny of the eye; 

 and, finally, the very important — probably preponderating — 

 part which the epidermis plays in the formation of the prin- 

 cipal ganglia. As the auditory organ is referred to the series 

 of principal ganglia^ the eye appears to belong to the epi- 

 branchial series. 



The works, already cursorily mentioned, of Van Wihje, 

 Froriep and Beard furnish guaranty that the develop- 

 mental processes, which I have described in Ammocoetes, 

 also essentially recur in Gnathostomata. These named have 

 not seen the separation of the first cranial nerve rudiment 

 (Anlage) into spinal and branchial nerves, cephalad of the 



