OF NATURAL HISTORY. 28^ 



Neither are Birds, in their progrefs from birth to maturity, ex- 

 empted from changes. Like quadrupeds, many birds are blind for 

 fome time after they are hatched. In this condition, how different 

 are their form and appearances from thofe of the perfedt animals ! 

 At firft, they are covered with a kind of down inftead of feathers. 

 Even after the feathers flioot, they are often of a colour different 

 from that which they acquire when full grown. The beautifully 

 variegated colours of the peacock's tail appear not till he arrives 

 at his third year *. Birds that have crefts, or wattles, live a confi- 

 derable time before they acquire thefe ornaments, or marks of di- 

 ftindtion. All birds annually molt, or caft their feathers, in the 

 fame manner as quadrupeds fhed their hair, the new pufhing out the 

 old. 



Frogs, and many other amphibious animals, undergo great chan- 

 ges in their form and ftrudure. When it firft efcapes from the 

 egg, a frog appears in the form of a tadpole, an animal with a large 

 roundifh head, and a comprefled or fiat tail, but totally deftitute of 

 feet and legs. In this ftate it remains a confiderable time, when the 

 two fore-feet begin to fhoot, and have an exadt refemblance to the 

 buds of trees. As their growth advances, the toes and legs are di- 

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

 they are fomewhat later in making their appearance. During the 

 growth of the legs, the blood being drawn into different channels, 

 the tail fuffers a gradual mortification, till at laft it totally vanifhes, 

 and" the tadpole is metamorphofed into a quadruped. Tadpoles 

 never come out of the water ; but, after their transformation into 

 frogs, they become amphibious, and occafionally frequent both land 

 and water. ,,, ;, 



t O o The 



* Linnaei Amoen. Acad. vol. 4. p. 368. 



