90 WILLIAM HARVEY 



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 pale-blooded tribes the heart pulsates sluggishly 

 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 pulsation; they seem rather to live after the manner of 

 vegetables, or of those other productions which are there- 

 fore 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 whenever the heart has a double ventricle, 

 there are always two auricles present, but not otherwise. 

 If you turn to the production of the chick in ovo, however, 

 you will find at first no more a vesicle or auricle, or pulsat- 

 ing drop of blood ; it is only by and by, when the development 

 has made some progress, that the heart is fashioned ; even so 

 in certain animals not destined to attain to the highest per- 

 fection in their organization, such as bees, wasps, snails, 

 shrimps, crayfish, etc., we only find a certain pulsating 

 vesicle, like a sort of red or white palpitating point, as the 

 beginning or principle of their life. 



We have a small shrimp in these countries, which is taken 

 in the Thames and in the sea, the whole of whose body is 

 transparent; this creature, placed in a little water, has 

 frequently afforded myself and particular friends an oppor- 

 tunity of observing the motions of the heart with the 

 greatest distinctness, the external parts of the body present- 

 ing no obstacle to our view, but the heart being perceived 

 as though it had been seen through a window. 



I have also observed the first rudiments of the chick in 

 the course of the fourth or fifth day of the incubation, in the 

 guise of a little cloud, the shell having been removed and 





