116 M. Dufour on the different modes 



Chapter II. — Stigmatic Aquatic Respiration. 



I have just described various modes of branchial respiration 

 always occurring in exclusively aquatic larvae. I proceed now to 

 describe a perfect insect which has the privilege of a completely 

 aquatic respiration, exercised not by branchiae but by stigmata. 



I know as yet only one small Coleopterous insect, scarcely a 

 line in length, which has presented this last mode of respiration 

 in a most undoubted manner : it belongs to the numerous family 

 of the Curculionidae, — it is the Phytobius hydrophilus, which I 

 have lately described as a new species. The larva, the nymph 

 in its cocoon, and the perfect insect, all three Uve, in the midst 

 of the waters, parasitic on the deeply merged stems of the Myrio- 

 phyllum spicatum. It is an aquatic species in the strict sense of 

 the word. 



The discovery of such a habitat, for a Curculio, was so new 

 and extraordinary a fact as greatly to stimulate my curiosity. 

 In order to observe at leisure its manoeuvres, its peculiar habits, 

 and especially its original mode of respiration, I placed a good 

 number of individuals of this Phytobius in a large glass, in which 

 I tried to imitate all the conditions of its native abode, and for 

 more than a month I kept them within sight upon my desk. I 

 had to take all imaginable precautions to obtain satisfactory evi- 

 dence of this unusual fact. Long and patient attention con- 

 vinced me that this insect remains constantly submersed, even 

 during the night. 



I watched all its movements in order to ascertain whether it 

 came to the surface of the liquid to inhale air, like the Hydro- . 

 phili, Dytici, Corisce, Nepa, &c., without success, although its 

 colour, a whitish gray, singularly favoured my investigations. I 

 assured myself also that it had not the faculty of enveloping 

 itself with a layer of air, like several insects inhabiting the water 

 and without natatory organs. It so happened that in this glass 

 vessel containing my Phytobii there were also some minute Dy- 

 tici, which I frequently observed to exsert the end of their abdo- 

 men in order to provide themselves with air, and a Parnus Du- 

 merilii which presented the curious spectacle of its brilliant aquatic 

 aerostat, its diving-bell. 



I contemplated my Curculio during its long periods of im- 

 mobility : my attentive eye followed it in its slow ambulations ; 

 I saw it at times scratching with its mandibles, browsing upon 

 the Myriophyllum ; but it did not attempt to come to the surface. 

 I surprised it one day, having lost the hold of its floating support, 

 swimming at some depth by the mere agitation of its feet, like 

 the dog, or rather like the horse. It did not seem distrest at 

 what I at first thought was an accident. I afterwards saw it — 



