SEGMENTS OF TRIGEMINAL NERVE-GROUP 283 
he describes a nerve (#., 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 
, 
/ 
Hy ul Or Il vel 
Fie, 113.—Ganeia oF THE CRANIAL NERVES OF AN AMMOCG:TES, 4 MM. IN LENGTH, 
PROJECTED ON TO THE Mrpian Prang. (After KUPFFER.) 
A-B, the line of epibranchial ganglia; aw., auditory capsule; c., notochord; Hy., 
tube of hypophysis ; Or., oral cavity; w.l., upper lip; 1.1. lower lip; vel., septum 
between oral and respiratory cavities; V., VII., IX., X., cranial nerves; 2., 
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 
