113 M. Dufour on the different modes 



XII. — On the different modes of Aquatic Respiration in Insects. 

 By M. Leon Dufour*. 



Respiration in insects is either atmospheric or aquatic. But 

 whatever be the mode of this respiration, the air respired is always 

 destined to circulate in ramified channels, in trachea, in a univer- 

 sal vascular lung which transmits it to all the viscera, to all the 

 tissues of the organism, with the definitive purpose of aiding 

 nutrition. This is the anatomical feature which is the most re- 

 markable and the most eminently characteristic of insects. This 

 circulation of air has no exception. 



The air may be inhaled either by external respiratory orifices, 

 stigmata, or by special organs, branchice, which extract it from 

 the surrounding water. 



The numerous class of Insects then shares with the higher 

 animals, the Vertebrata, this twofold mode of respiration, the 

 atmospheric and the aquatic. This is one of the numerous ex- 

 amples of the harmonies of creation. And as, according to 

 Leibnitz, nature never proceeds per saltum, I shall show in an 

 aquatic insect, a mode of respiration intermediate between the 

 atmospheric and the branchial. This is a new fact in science. 

 Here is another of these harmonies. As in the vertebrated ani- 

 mals, so you will find in insects, species so organized as to be 

 able to live both in the air and in water, — in a word, to be amphi- 

 bious. 



This is not all ; there are insects which pass the first period of 

 their life with a branchial respiration, and the second period, or 

 the adult age, with an atmospheric respiration. You have the 

 fellow of these organisms in some Batrachian reptiles. 



But nature is far from restricting herself to such uniformity 

 of plan as is sought to be imposed on her. She displays the 

 immensity of her power and her resources in the variety of 

 creatures, as in that of their mode of existence. By no means 

 all aquatic insects have a branchial respiration. This latter form 

 of respiratory apparatus is exclusively peculiar, as I have just 

 intimated, to certain larvse. No insect arrived at the perfect state, 

 at that completed state of the organism in which the reproductive 

 act must come into exercise, has a branchial respiration : at least 

 only one example of this is known, that of the Pteronarcys re- 

 galis, Newp., a Neuropterous insect from North America. All 

 the others, whatever be the medium they inhabit, earth or water, 

 and irrespective of the order to which they belong, breathe air by 

 the aid of stigmata ; whereas, among the vertebrated animals, 

 fishes are bom, grow, and multiply with a branchial respiration. 



* From the^Comptes Rendus, vol. xix. p. 763. 



