THE ANATOMY OF DORT:^. 127 



EoUs papulosa and in Avion ater, we believe it to exist in all the 

 more highly organized mollusca. 



The supra-oesophageal nervous centres in the mollusca are, in 

 some instances, so concentrated, as to have led to the idea that 

 thej form only one mass ; in others, the ganglion are more or less 

 distinct, and separate from each other. Doris is taken as the 

 representative of one class, Aplysia of the other, and on compari- 

 son of both the supra and infra-oesophageal ganglia of these classes 

 with each other, we find a perfect correspondence between them, 

 with the exception of the visceral ganglia. The single one in 

 Doris is represented in Aplysia by a pair of ganglia; situated in 

 the posterior part of the body, near the root of the branchi?e. 

 The supra-oesophageal ganglia, in the Lamelli-hranchiata, appear 

 homologous with those of Doris. 



Having determined the existence of a true sympathetic or 

 organic nervous system in Doris, we feel ourselves more in a 

 position to trace a parallelism between the oesophageal nervous 

 centres of Doris, and other mollusks similarly organized, and the 

 cerebro-spinal system of the Vertebrata, and accordingly we find 

 that there is a very close correspondence between them, even to 

 the individual pairs of ganglia, of which they respectively consist; 

 the general result being, that the whole of the ganglia grouped 

 around the oesophagus, in the above Mollusks, answers to the 

 Encejyhalon, and a small portion of the Enrachidion of the 

 Yertebrata. 



Organs of the senses. — The auditory capsules are microscopic, 

 composed of two concentric vesicles, the inner enclosing numerous 

 oval, nucleated otolithes. The eyes are minute, black dots beneath 

 the skin, attached each by a pedicle to a small ganglion. They 

 are made up of a cup of pigment, receiving from behind the nerve, 

 and lodging in front the lens, having in advance of it a cornea, 

 the whole enclosed by a fine capsule. We believe that we have 

 shown the dorsal tentacles to be the olfactory organs. The organs 

 of touch are, the general surface of the skin, but more particularly 

 the oral tentacle or veil. Taste is most probably located in the 

 lips and channel of the mouth, the tongue being a prehensile organ, 

 and ill-adapted as the seat of such a function. 



