190 Mijcellanea Curicfa. 



where begin to recede, and make way for the reft 

 to follow, but wou'd remain as hVd and im- 

 moveable as if they were actually fblid. But by 

 the Dilatation of the Thorax, room is made for 

 the Fluids to move, and by the Coarctation of 

 it, frefh motion is impreft, which is the main 

 Spring whereby the Circulation is let and kept 

 going.^ 



This reciprocal Dilatation and Contraction of 

 the fuperficial Dimenfions of the Body, feems fo 

 neceflary to Animal Life, that there is not any 

 Animal fo imperfect as to want it, at leaft none 

 to the inward Structure, of which our Anato- 

 mical Difcoveries have yet reach'd. For, tho' 

 moft kinds of Fi[h and InfeEts, want both move' 

 able Ribs and Lungs, and confequently have no 

 dilatable Thorax, yet that want is made up to 'em 

 by an Analogous Mechanifm, anlwering fufHci- 

 ently the Neceflities of their Life. 



Thofe Fifties which have no Lungs, have G/V/r, 

 which do the Office of Lungs, receiving and ex- 

 pelling alternately the Water, whereby the Blood- 

 Vejjels fuffer the fame alteration of Dimenfions, 

 that they do in the Lungs of more perfect Ani- 

 mals. 



The Lungs or Air-Veffels of Infects, are yet 

 exceedingly more different in Structure, Diftr*- 

 bution, and Situation from thofe of perfect Ani- 

 mals, than thofe of Fifties are, and yet in 

 their life and Action agree perfectly with 

 both; that is, receiving and expelling the Air, 

 and varying the Dimenfions and Capacities of the 

 Blood-VeJJels. Thefe having no thorax, or fe- 

 parate Cavity for the Heart and Air-Veflels, 

 have the latter diftributed through the whole 

 Trunk of their Bodies, by which they commu- 

 nicate 



