78 Cincinnati Society of Natural History. 



Succifiea ovalis Gould. Heart situated as in obliqua ; pul- 

 sation 150 to 155 per minute (extended). 



Succinea avara Say. Heart situated as in the two last spe- 

 cies ; pulsations regular, 130 per minute (extended). 



Lirnncza desidiosa Say. Heart situated near the umbilicus ; 

 pulsations quick and regular, 155 per minute (animal active). 



Limncea columella Say. Heart as in desidiosa ; pulsations 

 somewhat irregular, three or four being quick, followed by a 

 pause; 53 to 60 per minute (animal active). 



Limncea palustris Miiller. Heart situated about two-thirds 

 of the distance from the lower border of aperture, between 

 upper and lower margins of aperture; pulsations regular, 81 

 per minute (animal active). 



Limncea caperata Say. Heart as in desidiosa ; pulsations 

 irregular, varying from 129 to 133 per minute (animal active). 



Limncea stagnalis Iyinne. Heart as in desidiosa ; pulsations 

 irregular, varying from 37 to 48 per minute (animal active). 



In the foregoing experiments 39 species have been exam- 

 ined and several hundred specimens. The results are some- 

 what curious. In some species there is a wonderful degree 

 of constancy in the number of the beats, while in others they 

 seem to be quite erratic. One law applies equally to all, that 

 the more active the species the larger the number of pulsa- 

 tions ; and also with the same species, when in a contracted 

 condition the pulsations are fewer and more feeble than when 

 extended and active. The pelecypods are all sluggish, and 

 have a corresponding low pulse, while the majority of the 

 gastropods are active and have a high rate of pulse. The 

 average pulse of the Pelecypoda is 22 beats per minute, the 

 lowest record being 10 and the highest 36 (an exception is 

 found in Sphcerinm stamineum, which has a record of 57 to the 

 minute). In the Gastropoda the average is 98, the lowest 50, 

 and the highest 162. It is quite probable that during the 

 hibernating season the pulsations are reduced almost to noth- 

 ing, in order not to use up the vital force of the animaL The 

 writer has been unable to detect any movement of the heart 

 when the mollusk is in this condition. 



6 



