PLANARIA NIGRA. 33 



warmth of the air. A numher of planariae 

 mutilated on the twentieth of January 1803, 

 had hecome entire animals in the succeeding 

 April : but all the new parts were of a lighter 

 colour, which was long of approaching the 

 sable hue of the old : and it may be question- 

 ed whether they ever grow equally dark as 

 those regularly deepened by age. Thus we 

 see a black head, with a light coloured tail ; a 

 dark body, with a white head ; and one lon- 

 gitudinal half black as jet, while its corre- 

 sponding portion is of clear grey. The ele- 

 mentary parts of all animals seem colourless: 

 their future opacity is derived only from cer- 

 tain assimilations of extraneous substances, 

 the atmospheric influence, or supervening ri- 

 gidity of the parts. Pellucidity marks the 

 rudiments of life : fishes are transparent on 

 exclusion from the egg; insects are pale on 

 leaving the chrysalis ; their organs are in- 

 firm, and their senses obtuse. But scarce 

 have they experienced the genial effects 

 of the air, when their members expand, 

 strength is acquired, and instinct becomes 



