78 VIGNETTES FROM INVISIBLE LIFE. 



brownish, according to the nature of its food or 

 condition as to food -supply. This latter form is 

 sometimes, or rather generally, divided into two 

 species H. vulyaris and H. fusca : the former a 

 plump, well-fed, light brown fellow ; and the latter 

 white, thin, and attenuated. It is, however, highly 

 probable that the difference is entirely owing to 

 the question of food or no food ; for I have seen 

 the full and plump H. vulyaris, with its short 

 stumpy arms, too lazy to extend them far beyond 

 its own body, gradually change both in appearance 

 and action as its supply of food became less and 

 eventually was cut off altogether. It then lost flesh, 

 and in the endeavour after food gradually threw 

 out its arms further and further, until it w r ould 

 equal in extent any H. fusca in this its essential, 

 or supposed essential, specific distinction. 



The Hydra are composed of a soft, jelly-like, 

 cellular substance, capable of great extension and 

 change of form and colour. It is a living tube of 

 sarcode, having its principal concentration of power 

 at one end, which is regarded as the head, and 

 where is situated the only opening into and exit 

 out of this wonderful tubular body, and whence 



