144 HOW INSECTS BREATHE. 



conclusions of even Newport. M. Dufour remarks,* that 

 a gill is an organ especially adapted to aquatic respiration, 

 whose physiological function is to extract air from water, 

 and would, therefore, be useless to an entirely aerial animal. 

 He suggests, therefore, that they may be only the remains 

 of the branchiae of the nymph, retained — " obliterees, in- 

 fonctionables, simplement appendiculaires et "vestigiaires." 



Yet if we consider Newport's reasoning,! we must, I think, 

 come to his conclusion. 



There are eight sets of branchial sacs, or tufts distributed 

 over the pectoral surface of the thoracic segments and first 

 two segments of the abdomen. The three pairs of thoracic 

 spiracles are situated as usual ; the abdominal, however, are 

 false, and each lead into a small cavity. 



The habits of the insect, though not strictly speaking 

 aquatic, are quite in accordance with the structure of the 

 respiratory organs, for it lives under stones, in crevices of 

 rocks which are constantly wetted by the spray of falling 

 water, and in other damp places. 



This single exception to the otherwise universal rule, 

 that no perfect insect breathes by means of branchiae, may 

 well excite our wonder, and should teach us how cautious 

 we ought to be in all generalizations in Natural History. Con- 

 sidering also how many insects there are of whose anatomy 

 we may be said to be entirely ignorant, it may well be 

 that there are various other interesting modifications of 

 the respiratory organs with which we are as yet unac- 

 quainted. 



Passing now to the larval stages, we shall meet with much 



* Ann. des Sci. Naturelles — " Observations sur les Larves cles Neu- 

 ropteres," v. 17, p. 89, 1852. 



f On the Anatomy and Affinities of Pteronarcys Regalis, Linnean 

 Transactions, 1848, vol. xx. 



