SEGMENTS OF TRIGEMINAL NERVE-GROUP 



28 



he describes a nerve (x., Fig. 113), with four epibranchial ganglia, 

 which do not persist as separate ganglia, but either disappear or are 

 absorbed into the two main ganglia (Fig. 113). This discovery of 

 Kupffer's is very suggestive, for, as already stated, a transformation 

 takes place when the Ammoccetes is 5 mm. long, so that the 

 arrangement of the parts before that period is distinctly more 

 indicative of the ancestral arrangement than any later one. 



If we use the name plakodal ganglia to represent that part of 

 these ganglia which was originally connected with the skin, then 



Vx vn ix x 



Fig. 113. — Ganglia op the Cranial Nerves of an Ammoccetes, 4 mm. in length, 



PROJECTED ON TO THE MEDIAN PLANE. (After KUPFPER.) 



A-B, the line of epibranchial ganglia; an., auditory capsule; nc., notochord ; Hy., 

 tube of hypophysis ; Or., oral cavity; u.l., upper lip ; l.l. lower lip; vel., septum 

 between oral and respiratory cavities ; V., VII., IX., X., cranial nerves ; x., 

 nerve with four epibranchial ganglia. 



Kupffer's researches assert that in the larval Ammoccetes there were 

 seven such plakodal ganglia, one in front belonging to the foremost 

 trigeminal ganglion, two behind, parts of the hindmost ganglion, and 

 four in between, which do not exist later as separate ganglia. 



In accordance with the views put forward in this book, a possible 

 interpretation of these plakodal ganglia would be given as follows : — 



Beard, who, after Froriep, drew attention to this relation of the 

 cranial ganglia to special skin-patches, has compared them with the 

 parapodial ganglia of annelids, i.e. ganglia in connection with 

 annelidan appendages ; whether we are here obtaining a glimpse of 

 the far-off annelidan ancestry of both arthropods and vertebrates it 

 would be premature at present to say. It is natural enough to 

 expect, on my view, to find evidence of annelidan ancestry in 



