GASTEROPODA. 415 



haps in size, pour the secretion that they furnish into three dif- 

 ferent situations : the first into the esophagus, the second into the 

 oesophagus likewise, and the third into the gizzard, which forms the 

 first of three stomachal cavities. 



In Doris, a figure of which is given above, a still more extra- 

 ordinary arrangement is met with. One set of ducts derived from 

 the liver penetrate the stomach, and pour the bile into that cavity ; 

 while another large canal, equally given off from the liver, terminates 

 at the exterior of the body by an orifice situated in the vicinity of 

 the anus (fig- 185) ; and thus a part of the bile secreted would 

 seem to be expelled from the system as excrementitious matter, 

 a fact of no ordinary importance to the physiologist, as it would 

 itself go far to prove that the function of the liver is not merely 

 limited to the supply of a secretion of importance in the digestion 

 of food, but that it powerfully co-operates with the respiratory 

 system in purifying the circulating fluids by decarbonizing the 

 blood. 



(451.) Other secretions, apparently of an excrementitious cha- 

 racter, are furnished by many Gasteropods. Thus, in Aplysia a 

 glandular mass is imbedded in the opercular flap that protects the 

 gills ; from which, at the pleasure of the animal, a reddish liquor is 

 made to exude in sufficient abundance to obscure the water around 

 it, and thus conceal it from pursuit. Another gland furnishes an 

 acrid limpid fluid, that distils from an orifice near the oviduct ; 

 but the use of this last secretion is as yet unknown. 



(45#.) The scattered condition of the nervous ganglia, charac- 

 teristic of the HETEROGANGLIATA, is well exhibited in the pec- 

 tinibranchiate Gasteropods ; more especially as it not unfrequently 

 happens that the ganglionic centres themselves are of an orange or 

 reddish colour, while the nerves derived from them present their 

 usual appearance. 



In Buccinum the brain still occupies its usual position above 

 the oesophagus (Jig. 193, d), and gives off nerves to the organs of 

 sensation, and largfc twigs (c, c) to the eminently sensitive pro- 

 boscis. A large nervous mass placed beneath the oesophagus (*) 

 is connected with the former by several communicating nerves, that 

 embrace the oesophageal tube. Other ganglia, of smaller size (&, /, 

 w),are distributed in distant parts of the body, and supply the vis- 

 cera to which they are contiguous ; whilst they are connected among 

 themselves, and with the brain, by nervous cords passing from one 

 to another. 



