CHAP. II.] SEGMENTS OF ARTHROPODA. 101 



surprising that the animals living in No. XIV, for example, are scarcely dis- 

 tinguishable from those in No. XXIX, though the water in the latter was so strongly 

 alkaline as to feel soapy. The conditions of animal life in these two waters must 

 surely be very different, and yet no visible effect is produced. It is of course certain 

 that there are great differences in the physiology of these forms, for, as I have often 

 seen, animals (Copepoda, Cladocera, &c.) transferred from one water to another of 

 materially different composition, die in a few minutes, though the second water may 

 be inhabited by the same species; but in visible structure, the differences are for the 

 most part trifling and equivocal. 



