Mr. G. Newport on the existence of Branchice in Pteronarcys. 23 



to discover any orifice in the extremity of the filament itself, nor 

 any direct communication whatever between the external surface 

 and the ramifications of these tracheae, and I doubt much whether 

 any such direct communication exists. 



M. Pictet has found that branchiae are attached to the thorax 

 of the larva in all the species of Perla excepting P. virescens and 

 P. nigra J which circumstance seems to indicate some difierence 

 in the habits of these species. Now a like diiFerence exists between 

 the pupa oi Pteronarcys regalis and that oi Perla ahnormis, Newm., 

 which latter insect has not these branchiae ; and Mr. Barnstone, 

 who has most assiduously observed the habits of these species, in- 

 forms me that he found the first living constantly in the water 

 at the bottom of streams, but the latter was always hidden in 

 clefts of water-logged timber, the trunks of trees and other places 

 on the baijis, and that he has usually found the cast-ofi" exuviae of 

 the pupa "under stones along the banks of rivers.^^ This dif- 

 ference in the habits of the pupae leads to further inquiry in re- 

 gard to those of the perfect insects. P. regalis he states is a noc- 

 turnal species, being mostly found hidden by day under stones or 

 in damp places, and coming abroad on the wing only at night- 

 fall. Has this habit any reference to the persistence of the 

 branchiae, and the mode in which the aeration of the fluids is ef- 

 fected ? or are these persistent branchiae merely accidentally re- 

 tained organs, the functions of aeration being performed by other 

 means ? The existence of three pairs of orifices on the sternal 

 surface of the thorax seems at first to favour this latter conclu- 

 sion ; but it yet remains to be shown that these orifices have any 

 communication with the tracheae, since they are placed in the 

 middle of the sternal portion of each of the segments, between 

 the coxae, situations in which spiracles do not usually exist. This 

 question, therefore, I leave for the present for closer anatomical 

 investigation. 



In regard to the function of aeration being performed by these 

 branchiae in the perfect insect, I may remark, that it is of little 

 consequence to the preservation of animal life whether aeration of 

 the fluids of the body be efiected directly ^ by means of air received 

 into the body in lungs, or in spiracles and tracheae, or indirectly, 

 by means of water or vapour, that holds air intermixed with it, 

 through the agency of external branchial organs, in which case 

 the air is brought into contact with the fluids through the sur- 

 face of these organs in water equally well as in the open atmo- 

 sphere, when air is taken into the body through the spiracles. 

 The function of branchiae, or aquatic organs, is equally well per- 

 formed in the open air as in water, so long as the air is charged 

 with a sufiiciency of fluid to preserve these organs in a healthy 

 state. 



Some circumstances connected with the respiration of larvae 



