On the Pulsations of the Molluscan Heart. 



75 



Register of Observations. 



Anodonta grandis Say. A half dozen individuals of this 

 species were examined with some curious results. The first 

 two specimens had what appeared to be double pulsation, 

 which consisted first of a short, quick pulsation, followed 

 immediately by a long, slow pulsation. Thirteen long and 

 thirteen short throbs were counted, making a total of twenty- 

 six pulsations to the minute. In the other four individuals 

 fifteen regular beats were counted, and this is probably the 

 normal pulse. It is quite likely that the specimens first 

 examined were injured in being removed from the shell. 



Anodo?ita edentula Say. A number of specimens of this 

 species have been examined, and the records are very con- 

 stant. The pulsations were very regular, numbering ten to 

 eleven per minute. In this species the heart could be seen 

 beating for nearly half an hour after animal was removed 

 from the shell. 



Anodonta lacustris I^ea. The heart pulsations of this 

 species are unusually regular. In a number of specimens 

 examined the variation was but a single point, and that only 

 in one specimen. The record gave 29-30 beats per minute, 29 

 being the specimen which was below the normal. The num- 

 ber of pulsations is large for the genus. 



Anodonta ferussaciana Lea. Pulsations 16 per minute, with 

 no variation. All examinations made showed a wonderful 

 degree of constancy. 



Margarita?ia rugosa Barnes. This species is very slow and 

 sluggish in its circulation. The pulsations were regular and 

 slow, 13 per minute. 



Unio luteolus I^am. The movements of the heart may be 

 seen very plainly through the transparent walls of the peri- 

 cardium. The contractions in this species are particularly 

 wave-like. The pulsations are regular and number 16 per 

 minute. 



Unio gibbosus Barnes. The pulsations number 20 per 

 minute. Very regular. 



Unio undulatus Barnes. Pulsations regular, n per minute. 



Unio iris I v ea. Sometimes a double pulsation, a long one 

 followed by a short one ; 14 per minute. 



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