23 THE PHILOSOPHY 



fed into each other. By contradling and dilating thefe rings, 

 all the movement's of this kind are performed. The head, 

 in fome fpecles, changes its form every moment. It contra(Sts 

 or dilates, appears or difappears, at the pleafure of the animal. 

 Thefe motions arc permitted by the flexibility of the mem- 

 branes, or coverings of the head. In other fpecies, the form 

 of the head is permanent, owing to the hardnefs of the cover- 

 ings, which are fcaley or cruftaceous, and approaches nearer 

 to that of the more perfect animals. 



Many infers are deftltute of particular organs. Some want 

 eyes, ears, brain, and noftrils. Other have an acute fenfe of 

 fmelling, though we know not the form nor fituation of the 

 organ. The inferior fpecies of infects have no internal lungs, 

 but receive air by lateral pores, and fometimes by long tubes, 

 or tracheae, which protrude from different parts of the body. 

 Many infe6ls have no heart, or general refervolr for the re- 

 ception and propulfion of the blood. But we difcover by the 

 microfccpe, that their blood circulates by the pulfation of ar- 

 teries, and that their different fluids are fecreted by glands. 

 In a word, nature, in the firudlure and fundtions of animals, 

 defcends, by degrees almofi: imperceptible, from man to the 

 polypus, a being which, ever flnce its oeconomy and proper- 

 ties were difcovered by M. Trembley, has continued to afton- 

 ifh both phiiofophers and naturalifts. The ftru6lure of thfe 

 polypus, which inhabits frefli water pools and ditches, is ex- 

 tremely fimple. Its body conflfts of a Angle twbe, with long 

 ieutacula^ or arms, at one extremity, by which it feizes fmall 

 worms, arid conveys them to its mouth. It has no proper 

 head, heart, flomach, or inieftines of any kind. This fim- 

 plicity of flructure gives rife to an equal fimpliclty in the 

 oeconomy and functions of the animal. The polypus, though 

 it has not the diftinctlon of fex, is extremely prolific. When 

 about to multiply, a fmall protuberance or bud appears on 

 the furface of its body. This bud gradually fwells and ex- 



