216 THE bntomologist's record. 



at least unable to contract and close, and that these movements are 

 a gi'adual resumption of activity or of normal position, which is 

 probably that of closure. But I still think the closing has something 

 to do with the regulation of fluid pressure in connection with the 

 redistribution of plasma and expansion of appendages, then so actively 

 taking place. 



The hypothesis that the inner valve is merely resuming its normal 

 position and function, gains some support from the fact, that the outer 

 or surface valve is at the same time undergoing a contraction to its 

 normal aspect and form, and that both of these valves have been widely 

 stretclied l)y the whole process involved in the separation and removal 

 of the tracheal linings. So far the parallel between the two valves is 

 good, and justifies an argument from the one to the other. But the 

 parallel is far from complete, since the surface valve is entirely a 

 cutaneous, or rather chitinous and epidermal structure, and that 

 which is gradually contracting to its final narrow opening, is a 

 new structure, replacing the old which has been cast, and could not 

 therefore take its proper position before the old one, which occupied it, 

 was gone. The inner valve, on the other hand, is a more permanent 

 structure, consisting of dermal, tendinous and muscular structure. 

 "What it loses at the moult is merely its epidermal lining, of no 

 greater density than that lining the rest of the tracheal canals. 



The movements are certainly synchronous, with the general 

 muscular (vermicular) wave aflfectiug the whole insect, and having 

 something to do with the redistribution of fluids. 



The alteration in the proportion of parts that occurs within ten or 

 twenty, or rather more, minutes of tlie moult, is certainly very remark- 

 able ; for instance, I note in the case of Vhalera hucephala imme- 

 diately the moult takes place, the length of the pupa in sixteenths 

 of an inch is 17, divided into (1) 7 from anterior extremity to end 

 of wings, (2) 6 thence to hind margin of Gth abdominal segment, and 

 (3) 4 more to anal extremity. At intervals of ten minutes the 

 corresponding measurements were .- 



1. — At moult ... ... 7:6:4 



2.— After 10 minutes ... ... 7|: 5^: 4 



3.— After 20 minutes ... ... 8:5:4 



4.— After 30 minutes ... ... 8J: 4J: 4 



5. — After 40 minutes ... ... 9 : 4 -t* 4 



This is caused i)artly l)y the growth of the wings and appendages, till 

 they reach the hind margin of abdominal segment 4, partly by shrinkage 

 of segments 5 and 6. I am not able to say how far this growth of the 

 wings is due entirely to a process of growth, expansion, redistril)ution 

 of parts, or whatever it may be occurring in the cells of the expaudiug 

 part itself, or whether it depends entirely, or to a great extent, on fluid 

 pressure from the contracting portions of the insect, produced by 

 muscular action or otherwise, yet it would depend on this very much 

 whether the winking action of the tracheal valves has the subsidiary 

 function in connection with this process that I suggest. 



The analogy of the expansion of the wings (and in many cases other 

 appendages) of imagines, suggests that the fluid pressure hypothesis 

 is a correct one, since there is little doujjt that such pressure, aided by 

 the ingestion of a large quantity of air, is the effective cause of the 

 expansion of the imaginal appendages. 



