Gaspard on Helix Pomalia. 177 



§. 21. The blood of these animals must now call our attention 

 for a moment. This is not only contained in the organs of circu- 

 lation, but is poured out, particularly whilst the animal walks, 

 into the cavity containing the digestive and genital viscera, which 

 are bathed in the blood ; so that on cutting through the separation 

 between the trachea and abdominal cavity, an abundant and con- 

 tinued jet of this fluid is thrown out. Whilst the animal remains 

 at rest, and retired into the shell, the blood is not poured out in 

 the same manner.* This phenomenon struck me forcibly, and 

 I know of nothing analogous to it in other animals. The blood is 

 rather thick, but without viscosity ; it has a faint smell, a slightly 

 saline taste ; and is so abundant that each adult individual con- 

 tains not less than a dram and a half. It is of a delicate blue 

 colour, which is neither altered nor modified, by change of ali- 

 ment, by asphyxia, or by hibernation. It is miscible with water, 

 but of greater specific gravity, and falls to the bottom in visible 

 streaks or entire drops. AVhen exposed to the atmosphere, it 

 does not spontaneously congeal, like that of vertebrated animals, 

 but it separates by rest into two distinct fluids, the one blue, 

 which swims at the top, the other colourless and opake, remaining 

 at the bottom of the vessel ; in a few days it decomposes with 

 fetor. It is unaltered by muriate of barytes, and by alkohol, — is 

 simply discoloured by potash ; and by vinegar, and other weak 

 acids. But acetate of lead, nitrate of silver, and still more, ni- 



* This conclusion of Mens. Gaspard, I thought too curious and singular for 

 nie to pass it over without submitting it to the test of direct experiment. I 

 have therefore repeatedly and carefully injected the vessels of these animals 

 by the aor/a, but have never found any communication between the circulating 

 system and the visceral cavity. In fact, the fluid which the autlior mistook 

 for blood, is, I believe, nothing more than a large quantity of serum, effused 

 for the purpose of lubricating and protecting the viscera, and similar to that 

 which serves the same office in the thoracic and abdominal cavities of other 

 animals. May not the quantity which thus fills this cavity in the Snail, be in- 

 tended, by affording, as it were, a reservoir of moisture, to provide against tho 

 effects of extreme heat and drought, during which they often retire for a con- 

 siderable time into their shells, in a state of partial torpidity ? Thus performing 

 an office somewhat analogous to that of the fat in vertebrated animals, which 

 being absorbed during a long period of abstinence, supplies the place of food. 



T.B. 



