4418 Mollusks. 



provided, as is every other land mollusk, with a breathing-hole, into 

 which, at irregular intervals, air is admitted, though it continues for 

 the most part open, when the animal is in motion, closing instantly if 

 the smallest breath of air comes against it. This opening discloses 

 wonders when closely examined ; the cavity to which the breathing- 

 hole opens extends right through the upper part of the body, beneath 

 the mantle to the skin on the other side. Within this may be seen 

 part of the pulmonary vessels, the greater portion of the heart, and a 

 sac containing the arteries, through which the semitransparent blood 

 is poured to all parts of the body. The arterial sac is furthest re- 

 moved from the opening, and shows the pulsations in a remarkably 

 beautiful manner; in fact, the arteries themselves may be seen to be 

 slightly darkened by the flow of the blood at every stroke. The num- 

 ber of pulsations in the one I first examined was from 50 to 55 per 

 minute. In front of a portion of this sac is the heart, which, is a 

 whitish and almost opaque body, the lungs being spread over the upper 

 part of the cavity, and protected by the flat internal shell. Having 

 been very much interested with the above observations, I was led to 

 make further investigations and experiments on the circulating system 

 of a few of the other commoner mollusks, and the following is the re- 

 sult of some of these investigations. 



At a temperature of about 60° or 65° Fahr. the pulsations of Zonites 

 radiatulus are from 50 to 55 per minute ; of Z. crystallinus 60 to 65 ; 

 of Z. parus about 70 ; of Z. nitidulus 65 to 70 ; and of Z. alliarius 

 65 to 70. The pulsations of Helix hybrida, in an immature specimen, 

 were about 90 per minute ; the latter, however, was examined when 

 the temperature was about 70° Fahr. This may seem to some to be 

 a useless remark, and may perhaps excite a smile, but let them read 

 on, and I doubt not they will be as much surprised as I was at finding 

 what au effect a small amount of heat has upon the circulation of 

 these seemingly sluggish creatures. Let any one, after watching and 

 counting the pulsations of Z. alliarius at the above temperature, take 

 the same shell into his hand, and he will find that the pulsations are 

 very much accelerated almost instantly ; in fact, nearly doubled. The 

 pulse of Z. alliarius beats at the rate of 110 per minute. In Z. radi- 

 atulus I counted 100 per minute, and similar results were obtained 

 from the rest. From this 1 Was induced to proceed still further, and 

 see what effect the abstraction of heat had upon them : 1 found it 

 precisely the same as might have been expected from the above 

 results. 



By dissolving equal parts of saltpetre and muriate of ammonia in 



