Heart and Blood 35 



and like a living thing ; and nature in death, as 

 Aristotle l further remarks, retracing her steps, reverts 

 to whence she had set out, returns at the end of her 

 course to the goal whence she had started ; and as 

 animal generation proceeds from that which is not 

 animal, entity from non-entity, so, by a retrograde 

 course, entity, by corruption, is resolved into non-entity ; 

 whence that in animals, which was last created, fails 

 first ; and that which was first, fails last. 



I have also observed, that almost all animals have 

 truly a heart, not the larger creatures only, and those 

 that have red blood, but the smaller, and [seemingly] 

 bloodless ones also, such as slugs, snails, scallops, 

 shrimps, crabs, crayfish, and many others ; nay, even 

 in wasps, hornets, and flies, I have, with the aid of a 

 magnifying glass, and at the upper part of what is called 

 the tail, both seen the heart pulsating myself, and shown 

 it to many others. 



But in the exsanguine tribes the heart pulsates slug- 

 glishly and deliberately, contracting slowly as in animals 

 that are moribund, a fact that may readily be seen in 

 the snail, whose heart will be found at the bottom of 

 that orifice in the right side of the body which is seen 

 to be opened and shut in the course of respiration, and 

 whence saliva is discharged, the incision being made 

 in the upper aspect of the body, near the part which 

 corresponds to the liver. 



This, however, is to be observed : that in winter and 

 the colder season, exsanguine animals, such as the snail, 

 show no pulsations ; they seem rather to live after the 

 manner of vegetables, or of those other productions 

 which are therefore designated plant-animals. 



It is also to be noted that all animals which have a 

 heart, have also auricles, or something analogous to 

 auricles ; and further, that wherever the heart has a 

 double ventricle there are always two auricles present, 

 but not otherwise. If you turn to the production of 



1 De Motu Animal, cap. 8. 



