CIRCULATION OF THE BLOOD 137 



in a state of higher preparation. The defects of either 

 extreme are supplied and compensated by this arrange- 

 ment of the veins. 



CHAPTER XVII 



THE MOTION AND CIRCULATION OF THE BLOOD ARE CON- 

 FIRMED FROM THE PARTICULARS APPARENT IN THE 

 STRUCTURE OF THE HEART, AND FROM THOSE THINGS 

 WHICH DISSECTION UNFOLDS 



I DO not find the heart as a distinct and separate part 

 in all animals; some, indeed, such as the zoophytes, have 

 no heart; this is because these animals are coldest, of one 

 great bulk, of soft texture, or of a certain uniform same- 

 ness or simplicity of structure; among the number I may 

 instance grubs and earth-worms, and those that are en- 

 gendered of putrefaction and do not preserve their species. 

 These have no heart, as not requiring any impeller of 

 nourishment into the extreme parts; for they have bodies 

 which are connate and homogeneous and without limbs; so 

 that by the contraction and relaxation of the whole body 

 they assume and expel, move and remove, the aliment. 

 Oysters, mussels, sponges, and the whole genus of zoophytes 

 or plant-animals have no heart, for the whole body is used 

 as a heart, or the whole animal is a heart. In a great 

 number of animals, almost the whole tribe of insects 

 we cannot see distinctly by reason of the smallness of the 

 body; still in bees, flies, hornets, and the like we can per- 

 ceive something pulsating with the help of a magnifying- 

 glass; in pediculi, also, the same thing may be seen, and 

 as the body is transparent, the passage of the food through 

 the intestines, like a black spot or stain, may be perceived 

 by the aid of the same magnifying-glass. 



But in some of the pale-blooded and colder animals, as 

 in snails, whelks, shrimps, and shell-fish, there is a part 

 which pulsates, a kind of vesicle or auricle without a 

 heart, slowly, indeed, and not to be perceived except in 

 the warmer season of the year. In these creatures this 

 part is so contrived that it shall pulsate, as there is here 

 a necessity for some impulse to distribute the nutritive 



