IXVl INTRODUCTORY OBSERVATIONS, 



There is a remarkable fympathy often beheld 

 between fome parts of animals that are continually 

 reproducing, and thofe which never regenerate. 

 No part is more conftantly reproduced than the 

 beard ; its progrefs is frequently perceptible in a 

 few hour^ ; but caftration puts an end to it for 

 ever. Many animals reproduce the horns every 

 year ; but caftration of the animal without them 

 prevents their growth : and it is faid, the caftra- 

 tion of an adult male prevents them from faUing 

 again. This operation produces a fingular effedl 

 on the frame : a vifible change enfues j the in- 

 crement of certain parts terminates, while others 

 extend to an immoderate fize. Even the mind 

 is materially affeded. 



Throughout nioft of the animal fcale, there is 

 a general reproduftion of the parts which are of 

 a fmiilar nature. The fkin, nails, hair, feathers, 

 horns, and fcales, have a great analogy to each 

 other. Some of thefe, which, in particular ani- 

 mals, are renewed by a partial and continual 

 change, are loft and repaired by others all at 

 once. Serpents and caterpillars caft the whole 

 fliin. A caterpillar will in a fliort time repro- 

 duce fix or feven, — within a few months. The 

 lobfter annually throv.s off its lliell, and acquires 

 a new one ; and, with the ftiell, it alfo lofes the 

 (lomach. The feathers of birds are changed 



once 



