114 ' M. Dufour on the different modes 



The internal walls of the rectum of our large larvae are tra- 

 versed, throughout their length, by six regular and symmetrical 

 columns, converging at the two extremities, each formed of two 

 series of superposed or imbricated laminae. These laminae con- 

 stituting the organ, traced to their intimate or elementary texture, 

 are reduced, definitively, to a network, a subtle canvas of trachean 

 divisions. These latter are attached by successive anastomoses 

 to the branches, ramifications and trunks, which together con- 

 stitute the general system of the aerial circulation. It is certfiinly 

 more easy to follow up these connexions, these fine vascular 

 anastomoses, in this minute animal, than in man or in the ox, 

 and for a scalpel and practised eyes there is scarcely a possibility 

 of mistake. 



. The last term of the organic composition would therefore be, 

 in the branchiae of the insect, as in those of the fish, a vascular 

 woof ; giving to this last word only its rigorous etymological or 

 anatomical value. Only, in the fish, it is Mood, and in the insect, 

 air which is contained in the vessels of this woof. 



The insect and the fish have consequently branchiae. M. Du- 

 vernoy, in his just physiological appreciation of the respiratory 

 apparatus in these two classes of animals, has called that of insects 

 pneumatic branchiae, a significative epithet, which, expressing the 

 a'eriferous function, establishes the differential character with the 

 branchiae of fishes, which are sanguiniferous. 



Pursuing this parallel of the branchiae, we see that those of 

 fishes are placed on the sides of the head, and the water sub- 

 mitted to their action penetrates the mouth ; it is a hyobranchial 

 apparatus, according to the expression of M. Duvernoy. In our 

 larvae, the rectum is the receptacle of the branchiae, and the water 

 is received by the anus ; the apparatus is thus rectobranchial. 



I shall conclude this notice by an anatomical fact the more in- 

 teresting, as it offers the most perfect analogy with what is ob- 

 served in the branchiae of fishes. After macerating in water, for 

 two days, a larva dissected with a view to trace the mode of con- 

 nexion of the vessels of the branchial lamina, I perceived that my 

 pincers drew with ease a large shred of a hyaline membrane, which 

 evidently was detached from the internal side of the rectum. I 

 examined scrupulously this membranous shred, and what was my 

 agreeable surprise to observe in it a serial arrangement of plaits 

 representing the free edges of the branchial laminae with all the 

 details of their texture ! I then eagerly directed my lens to the 

 corresponding and denuded portion of the rectum ; I found in 

 place the branchial laminae with all their anatomical attributes, 

 but more distinct than before that exfoliation or decortication. I 

 repeated this experiment, and obtained the same results. In 

 fishes, the laminae and the ridges of the branchiae are similarly 



