3SS Sir E. Home's Additions to an Account 



laterally connected to the great muscle that shuts the shell, so 

 that whenever that muscle is actively employed, its lateral swell 

 presses against the heart, and forces out the blood, and by this 

 means gives activity to the circulation, at the only time in 

 which an increased circulation is particularly required. 



In the Muscle, the heart can hardly be said to be distinctly 

 divided into auricle and ventricle ; but to consist of an oval 

 bag, through the middle of which the lower portion of the 

 intestine passes. Two veins from the gills open into the heart, 

 one on each side, these may be considered as the auricles. 



The coats of the ventricle are very thin, so as to have little 

 power of propelling the blood ; but this weakness appears to 

 be compensated by the effect of the contraction and relaxation 

 of the intestine contained in their cavity. This circumstance 

 renders it probable, that the circulation goes on with activity 

 while the processes connected with digestion are employed ; 

 but when the intestines are empty, there being no supply of 

 nourishment, the circulation is not only very languid, but may 

 possibly be entirely stopped. 



In the caterpillar, the blood cannot be said to circulate, but 

 is carried from one end of the animal to the other, in a tube 

 which may be either called heart or artery, by a species of 

 peristaltic motion. This ebbing and flowing of the blood, if 

 such a term can be admitted, is greatly increased by the pres- 

 sure upon the different portions of this tube, produced by the 

 action of muscles employed in the progressive motion of the 

 animal, so that the supply of blood to the different parts of the 

 body is proportioned to the demand, which arises out of the 

 bodily exertions. 



