126 On Sicbaquatic Insects. 



the most part, they frequent still waters, and their movements are 

 not influenced by the agitated state of the fluid in which they reside. 



But there are other insects which pass a great portion of their 

 lives under water without possessing the power of swimming about, 

 and thus obtaining at will due supplies of air ; and there are others 

 which, in addition to this deficiency, are inhabitants of situations 

 which for hours, days, and even weeks are entirely covered by the 

 rolling tide of the sea, it being only at the period of neap-tides that 

 the spots where they are found are left uncovered by water. 



M. Dutrochet has endeavoured to explain the manner in which res- 

 piration is effected in the first of these cases, in a memoir upon the 

 larva of a moth, Hydrocampa potamogeta, read before the Acade- 

 mie des Sciences, which, as well as the pupa, resides constantly, 

 although provided with spiracles and not with branchiae, beneath the 

 surface of stagnant water. " II arrive pour cette chenille," 

 according to this author, " qu' epuissant par l'act de la respiration 

 l'oxygene de l'air atmosph£rique qui l'environne l'azote restant se 

 dissout dans l'eau et en extrait du gaz oxygene. Mais en meme 

 temps le gaz acide produit par la respiration se dissout aussi dans 

 l'eau et en extrait l'air atmospherique, dont l'oxygene sert naturel- 

 lement a la respiration et dont l'azote repare la perte du gaz azote 

 dissous." This may indeed perhaps be considered as the real solu- 

 tion of the chief inquiry, but there are so many differences both of 

 economy and structure in the subaquatic insects, that it must be 

 evident, that by minutely investigating each, we may arrive with 

 greater certainty at the general truth. Moreover, as in the case of 

 those natatorial species which from time to time come to the sur- 

 face of the water for fresh supplies of air, the respiratory process is 

 probably different from those which are constantly beneath its sur- 

 face, as in the larva of the water moth above-mentioned. We may 

 consider those species which, at certain periods, do obtain supplies of 

 fresh air, but in such small quantities as not to last for their con- 

 sumption for the long space of time they may be submerged, as oc- 

 cupying an intermediate station between these two groups breathing 

 fresh air at one period, and oxygen disengaged from, water at another. 



Of this latter class one of the most interesting species is the 

 Aepus fulvescens, a minute carabideous insect found upon the shores 

 of France and England, and whose economy has been traced by M. 

 Victor Audouin in his "Observations sur un insecte qui passe une 

 grande partie de sa vie sous la mer," published in the Nouvelles 

 Annales du Museum d'Histoire Naturelle," Vol. iii. p. 117- This 

 insect is not clothed with a coat of plush on its underside ; but when 

 examined with a lens its head, thorax, legs, antennae, and abdomen 



