GASTEROPODA. APLYSIAD®. 31 
The syphon produced to the right side of the head. Shell 
situated rather behind the middle of the back. Foot slightly 
produced behind. 
This animal was likened to a hare by the ancients, who 
affirmed that it was endowed with highly poisonous qualities. 
This fable was believed by Linné, who named the only species 
known in his time, depilans, a term which was applied by Pen- 
nant to the British Aplysia, the smell of which he asserts to 
be extremely nauseous. 
The Aplysia, as Milian has observed, bear a general appear- 
ance in their external form to a Pomatia divested of its shell. 
The head is situated at the extremity of a short neck, which is 
retractile. The mouth is vertical ; the lip on each side is pro- 
duced into a tentaculum. At the anterior bases of the dorsal 
tentacula are situated the eyes. Underneath the right side of 
the operculum is situated a sort of gland, which secretes the 
purple fluid for which it is so celebrated. The anus terminates 
at the hinder extremity of the attached part of the lid. The 
gland which secretes the supposed poisonous liquor opens be- 
tween the anterior attachment of the lid and the right dilata- 
tion of the mantle, by an aperture common to it and to the 
oviducts. 
The anatomical structure has been examined by Cuvier, and 
is very interesting in a physiological point of view. 
The brain is situated over the cesophagus, having a three- 
lobed ganglion on each side, brought into connexion with it by 
three nerves. These ganglia are connected by a nerve which 
passes round the cesophagus and completes the nervous collar ; 
and again by another nerve which embraces the great arterial 
trunk. The brain is united to a third ganglion, situated under 
the fleshy mass of the mouth, by two nerves. The lateral 
ganglia are again brought into connexion by a nerve which 
passes round the great artery. The suboral ganglion receives 
four nerves on each side; one pair from the cesophagus and 
salival glands, and three from the muscles of the mouth. The 
brain itself receives three pairs of nerves from the head: two 
receive branches from the male organ, and from the dorsal 
tentacula; the latter receive the optic branch. The lateral 
