74 ON PSYCHOPTERA PALUDOSA. 



que la difference de leur longueur et de leur emplacement ne 

 proviennent que de ce que, dans I'etat de ver, ce canal traversait 

 sous la peau de I'insecte, la longueur de son corps, pour aller 

 s'inserrer dans ce qui devoit devenir le haut du corselet de la 

 nymphe ; et qu'apres avoir quitte la peau de ver pour revetir la 

 forme de nymphe, cette partie du canal de la respiration que la 

 peau du ver couvrait s'offrant a decouvert, fait paraitre, par la ce 

 canal d'autant plus longue et attache au corselet. La reunion des 

 deux files de vaisseaux bruns qui vont sous la peau du ver de la 

 queue jusque pres de la tete et s'abouchent a cet endroit I'un avec 

 I'autre, et qui dans cet etat ne paroissent etre que ce meme canal 

 de la respiration continue semble confirmer cette ide'e, quoique 

 alors on ne convolve pas aise'ment par quelle mechanisme deux 

 vaisseaux, auparavant separes se sont re'unis pour n'en former 

 ensuite plus qu'un, ou se sont joints sous une meme enveloppe." 



The whole of this pother arose from the fact that Lyonet did 

 not perceive that the respiratory filament of the pupa was not a 

 single organ, but that it was one of a pair, of which one only is 

 developed, the other remaining rudimentary, see Fig. 12. They are 

 the superior pro-thoracic processes, and correspond on the pro- 

 thorax to the wings and halteres on the succeeding two segments. 

 Their development, however, ceases with the pupa stage, being 

 totally suppressed in the perfect insect. 



They are both rudimentary in, the pupa of the Blow Fly, and but 

 poorly represented in that of the Crane Fly. In this insect one 

 only is fully displayed, but in the pupa of the Gnat and CoretJwa 

 pliimicornis they are both seen to the greatest advantage. In all 

 cases where they are developed they subserve the process of respira- 

 tion. Lyonet says that the terminal portion of the filament of Fsy- 

 choptera is flattened and twisted into a helix, and that the insect is 

 capable of lengthening it by unrolling the coil to suit the depth at 

 which it lies in the water, and of shortening it again when the 

 necessity has passed away. I have not observed this, nor do I 

 quite see how it is to be accomphshed ; but the statement may, 

 nevertheless, be correct. The corkscrew twist I indeed recognise, 

 but not the knotted thread extending along the wall of the filament, 

 by which Lyonet further states its extension or retraction to be 

 effected. 



