XVlll INTRODUCTORY OBSERVATIONS. 



brain will' often occafion inftant death ; but va= 

 rious animals will live long, not only after the 

 whole has been fcooped from the cavity of the 

 Ikull, but after the head itfelf is cut off. 



In the larger animals, where diffedion may be 

 ufed, it is in the power of the anatomift to lay 

 every mufcle, tendon, and blood veifel, bare. 

 In thofe fo minute as infufion animalcula, where, 

 inftead of each part, the entire whole is in gene- 

 ral hardly vifible, the philofopher muft fome- 

 times be fatisfted with the moft rational induc- 

 tions from what he beholds, and analogical rea- 

 foning, if that is ever to be admitted. — The dif- 

 ferent functions of animalcula are probably per-' 

 formed by means analogous to thofe of other 

 animals. The courfe of fome, which are v/ithout 

 perceptible external organs, proportionally ex- 

 ceeds the fwiftefl flight of birds ; confequently, 

 they mull have confiderable ftrength. Whether 

 their motion proceeds from curvature, leaps, or 

 undulations, it can only be effefted by impulfe 

 againft the water j and we may reafonably infer, 

 that fome mufcular movement is the principle, 

 or that the ftrength proceeds from fomething cor- 

 refponding to mufcles. The great fource of mo- 

 tion among v/orms and aquatic animals, deftitute 

 of feet and fins, is undulation. In this manner 

 is the progreffion- of all ferpents, eels,, and many 



other 



