of Aquatic Respiration in Insects. 115 



covered with a membrane furnished by the buccal mucus, as has 

 been especially shown by MM. Duvernoy and Rosenthal. 



Let us devote a few lines to the comparative physiology of this 

 beautiful apparatus. 



As above stated, these larvae with rectal branchiae imbibe and 

 eject the ambient water by the anus. There is, therefore, alter- 

 nate ingress and egress of the liquid, as there is ingress and 

 egress of the air in atmospheric respiration ; but in this double 

 movement there is not that regularity, that isochronism, which 

 is observed in the respiration of large animals. The water must 

 remain in the rectum in order to bathe the branchiae, for the 

 accomplishment of the secretion of the vital air. The inspiration 

 and expiration are effected by the mechanism of an external 

 apparatus, the different pieces of which open and shut at the 

 will of the animal. It is this mechanism that Reaumur called 

 " unjeu de piston." 



I have just said that the branchiae are clothed or lined by the 

 mucus of the rectum ; it is this mucus therefore which, alone, in 

 direct and immediate contact with the water, effects, by its vital 

 properties, by an exquisite elective sensibility of its organic 

 chemistry, the separation of the respu*able air; this it is which 

 filters it, transmits it, and delivers it to the vascular woof of the 

 branchial laminae. Hundreds of these latter incessantly pay their 

 aerial tribute to the great trachean channels which, like so many 

 arteries, circulate, to the extreme limits of the organism, this 

 vital air which imparts the assimilating faculty to the nutritive 

 fluid, everywhere diffused or infiltrated. 



Let us see whether, in the large animals with hyobranchial 

 apparatus, nature does not adopt, with a few modifications, easily 

 explained, the same process. What takes place in the respiratory 

 act of fishes ? Have they not also branchial laminae, covered with 

 the buccal mucus, which abstract from water the respirable air ? 

 Does not the oxygen taken from the ambient liquid serve to give 

 the assimilating condition to the nutritive fluid? Up to this 

 point do we not see, in the fish as in the insect, the same series, 

 the same succession of functional acts, the same physiological 

 object ? In what then consists the difference ? Evidently in the 

 existence of a sanguineous vascular circulation in the fish, and in 

 the absence of this same circulation in the insect. And since 

 nature had substituted a circulation undoubtedly of air for a cir- 

 culation of blood, must she not, in consequence of her equal 

 solicitude for the maintenance of life in two organisms so distinct, 

 know how to reconcile the means and the end ? The nutritive 

 fluid not being able to go and seek the air, the air comes to seek 

 it in order to combine with it. 



