Affinities of Pteronarcys regalis. 435 



thoracic spiracle of the left side (fig. 6) has the anterior valve convex, and 

 bounded by a soft, thickened, pad-like, semicircular margin, and resembles 

 the upper lid of the human eye ; the posterior valve, on the contrary, has its 

 margin somewhat rigid, is deeply excavated, semilunar, and extended for- 

 wards at its superior angle into an elongated, slightly flattened broad process 

 or caruncle, to the posterior border of which is attached a broad levator 

 muscle, which opens or retracts the valve (fig. 8). The inferior angle of this 

 valve has also a small caruncle, which projects slightly over the anterior valve 

 when the spiracle is completely closed, but which has almost disappeared 

 when the spiracle is expanded. The closing of the spiracle seems to be 

 effected by circular fibres in the tegument, very similar to those of the orbicu- 

 lar muscle of the eye in f^ertebrata, attached (as shown in fig. 7) at the anterior 

 superior angle. The closure of the spiracle is completed (as in fig. 6) by the 

 action of other muscles on the tegument behind the posterior valve, by which 

 this is carried forwards, and its process is made to cover and shut down like a 

 lid on the anterior valve, so as to render it impossible for anything to penetrate 

 into the chamber of the spiracle when the valves are completely closed. This 

 structure indicates that the action of these respiratory orifices is under the 

 control of the will or instinct of the insect, as well as of the reflected influence 

 of the nervous power on the application of stimuli, and probably has some 

 direct reference to the habits of this anomalous insect. 



But what peculiar modification in oeconomy can we infer from this duality 

 of respiratory organs, branchiae and spiracles in the same individual ? Can 

 it be that the imago Pteronarcys ever actually re-enters the water for any 

 purpose after it leaves it, as Mr. Barnston has informed me it does, to change 

 to an imago under stones, on the banks of rivers ? Does it ever as a perfect 

 insect dive in search of food ? or, besides residing constantly in the most damp 

 situations, does the female, creeping down the stems of water-plants, as is 

 said to be the habit of Phryganea grandis*, descend beneath the surface of 

 the stream to deposit her ova, or the male to assist in her operations ? These 

 are questions which only a close attention to the habits of the insect can solve, 

 whilst the duality and the peculiar structure of its respiratory organs admit 

 of their being entertained. That the structure of the spiracle may have refer- 



* Curtis, British Entom., fol. 592. 



