204 NATURAL HISTORY. [cH. XIV. 



waters, its form, under the states of larva and pupa, 

 varies so little as to deceive all but the keen eye of 

 an entomologist. Nevertheless, the winglets at- 

 tached to the pupa (fig. 1), will in vain be sought 

 for in the larva (fig. 2) ; in every other respect 

 there is similarity of form and of function. Some 

 of these worms pass their lives in habitations, each 

 one in his own. This is nothing but a hole formed 

 in the bed of a river ; others, on the contrary, may 

 be termed wanderers ; and they are sometimes seen 

 to swim, sometimes to walk on the various sub- 

 stances found in the water; and sometimes they 

 remain tranquil and concealed under a stone. 



Those which are stationary offer the spectator a. 

 very amusing spectacle. On each side of the body 

 of the insect little prolongations gush out, which are 



moved with the rapidity of lightning, described as 

 fins by some ; while, on the contrary, others have 

 regarded them as oars ; and the little insect thus 

 fashioned has been compared to an antique galley. 

 But a moment's consideration will suffice to rectify 

 the error ; for it is observed, that the time during 

 which the supposed fins or oars are in the greatest 

 agitation, is that at which the larva is in repose. • 

 The oars or fins, however, are the instruments by 

 which the insect breathes its lungs. To those who 

 are not familiar with the study of comparative anat- 

 omy, it will appear strange that the lungs should be 

 placed on the outside of the body of any animal, and 

 that the function of respiration should be performed 

 by a rotatory motion of little tubes. Nevertheless, 



