PLANARIA VELOX. 1S3 



rium which another season would bring to 

 maturity. 



Prosecution of this enquiry was inter- 

 rupted, from the total evaporation of the 

 marsh where the animals had been found, 

 by an uncommon drought during summer 

 1813. Thus the race may be extirpated 

 there, unless, which is not improbable, the 

 revival of humidity shall promote the ex- 

 clusion of eggs accidentally preserved, and 

 which have not lost the latent principle of 

 vitality. 



Planar ia Edinensis, Fig. 18. — The differ- 

 ent genera of animals are constituted by 

 uniting individuals bearing the greatest re- 

 ciprocal analogies in habits or conformation 

 under some common characteristic. But 

 a subordinate distribution into species soon 

 becomes necessary, from more attentive 

 examination discovering peculiarities in one 

 which are wanting in another. The plana- 

 rise of the former division are united by 

 structure, in a proboscis protruding from 



