21)4^ THE PHILOSOPHt 



colours ofthe peacock's tail appear not till he arrives at lils' 

 third year *. Birds that have crefts, or wattles, live a con- 

 fiderable time before they acquire thefe ornaments, or marks 

 of diftincStion. All birds annually molt, or caft their fea- 

 thers, in the fame manner as quadrupeds ihed their hair, the 

 new pufliing out the old. 



Frogs, and many other a?nphibious animals, undergo great 

 changes in their form and il:ru6lure. When it firll efcapes 

 from the egg, a frog appears in the form of a tadpole, an 

 animal with a large roundifli head, and a comprelTed or flat 

 tail, but totally deftitute of feet and legs. In this ftate it re- 

 mains a condderable time, when the two fore-feet begin to 

 fhoot, and have an exa-ft refemblance to the buds of trees. 

 As their growth advances, the toes and legs are diftinguilha- 

 ble. The fame procefs goes on with the hind-legs, only 

 they are fomewhat later in making their appearance. Dur- 

 ing the growth of the legs, the blood being drawn into dif- 

 ferent channels, the tail fufFers a gradual mortification, till at 

 lafi: it totally vaniflies, and the tadpole is metamorphofed 

 into a quadruped. Tadpoles never come out of the water ; 

 but, after their transformation into frogS;, they become am- 

 phibious, and occalionally frequent both land and water. 



The cntjlaceous tribes, as lobfters, crabs,, &c. belide the dif- 

 ferent appearances they affume while growing to perfection, 

 caft their fhells every year. When this change is about to 

 happen, they retire into the crevices of rocks, or flielter 

 themfelves below detached ftones, with a view to conceal 

 and defend their bodies from he rapacious attacks of other 

 fillies. After the fhells are caft, the animals are exceeding-* 

 ly weak and defencelefs. Inftead of their natural defence 

 of hard ftiells and ftrong claws, they are covered only with ^ 

 thin membrane or fliin. In this fcate they become an eafy 

 grey to almoft every fifh that fwims. The Ikin, however, 

 * Liimaei Aaiocn. Acad, vol, 4. p. ^dZ, 



