490 Mr. Garner on the Nervous System of Molluscous Animals. 
branchio-visceral. The foot has become too insignificant to require appro- 
priate ganglia. Though there are in this animal, and in some species of Doris, ` 
no eyes, the author thinks he has found the rudiment of them in two minute 
black spots which he has noticed, one on each side the brain; and he infers 
that so unusual a circumstance must arise from the pigmentum nigrum exist- 
ing on the brain before the external eye is developed. These spots mark the 
superior ganglia to be the cerebral, and we find the tentacles supplied from 
them. Externally the nerves are derived which supply the mantle, branchie, 
and viscera. In Doris and Eolida (fig. 5.) the same conformation exists. 
According to Cuvier the four ganglia are quite separate in Tritonia; and it 
would appear, from the observations of the same anatomist, that the nervous 
system of the genera Phyllidia, Onchidium, Tethys, Testacella and Pleuro- 
branchus is more or less upon the same plan. The pharyngeal ganglia are 
often small, but exist as usual. 
The nervous system of the Aplysia, which is not figured in the plates 
accompanying this paper because it is so minutely described by Cuvier, is 
particularly interesting. The cerebral or sentient ganglia, giving origin as 
usual to filaments forming the pharyngeal ganglia, are conjoined, as in other 
naked Gasteropoda, into one situated above the cesophagus. The two late- 
ral ganglia give off internal filaments to the foot, and external ones to the 
mantle. It will be seen, as we ascend, that there are separate ganglia for 
the foot, mantle and branchize. In the Aplysia there is, besides, another gan- 
glion,—the one supplying the branchize and visceral organs at the posterior 
part of the body. That each of the lateral ganglia is in reality composed of 
two, appears from its supplying the two parts above mentioned, which, in most 
of the Gasteropoda and in the Cephalopoda, have separate ganglia for each: 
besides, the fellow ganglia are connected together by two separate filaments, 
and between them the aorta passes, which in many of the higher Gasteropoda 
and in the Cephalopoda distinguishes by its course that part of the ring which 
supplies the foot from that which supplies the mantle and viscera. Lastly, 
each lateral ganglion is connected to the sentient lobe by three nerves, being 
those which it receives from the pedal and from the branchial ganglia, and 
from that of the mantle. 
In Bullwa (fig. 9.) we find the pedal ganglia (B.) distinct from the two sup- 
