Affinities of Pteronareys 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 Fa 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 economy can we infer from this duality 
of respiratory organs, branchie and spiracles in the same individual? Can 
it be that the imago Pferonarcys 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 
 inseet 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. 
