extent it does in Euchlo'e, Callidryas, etc., just as we have to do in 

 the case of the nose and eye spines of Nymphalids, Papilionids, 

 etc., of various species on Papilionidoe, the remarkable processes of 

 the White Admirals, etc. 



We may just glance at the pupa of Sc. libairix. We see here that 

 Poulton's line gives us the form of the wing of the imago, and that 

 the pupal wing margin is tolerably close to it at either angle, but is 

 much behind it where the hind margin of the wing is hollowed out. 

 The pupal wing margin does not here follow a regular sweep from 

 apex to anal angle, but is slightly hollowed out where the imaginal 

 wing marked by Poulton's line is much hollowed. The fourth abdo- 

 minal segment has assumed some little irregularity to accommodate 

 itself to this excavation of the wing margin. This shows that the 

 wing margin and Poulton's line have a strong tendency to work 

 together when they are relieved from the pressure of the environ- 

 ment to which the exposed pupae of butterflies are subjected. It 

 appears also to prove that since they can vary together so much, 

 they would have absolutely coincided throughout the mass of the 

 Lepidoptera had the one been the pupal reminiscence of a former 

 stage of the other, or a mere pupal part having no direct relationship 

 to the imago, one or other of which must be the meaning of 

 Poulton's assumed basis. 



In the case of Sc. libatrix, I do not mean to be understood to 

 regard the marginal portion of the pupal wing as having been left 

 by Poulton's line, because it could not follow it at the rate at which 

 it moved, but that its failure to follow it absolutely was due to the 

 pupal necessity of a proper apposition to the fourth abdominal 

 segment in order to a due outline to the pupa, and that the present 

 position is a compromise between the desire of this margin to retreat 

 and the reluctance of the abdominal surface to supply all the 

 necessary modification. 



These considerations, I think, enable us to see what is the question 

 before us. Professor Poulton is right as to the inner line (Poulton's 

 line) corresponding to the outline of the imaginal wing, blurred and 

 simplified, either by the less development of the pupal structures, 

 and by no means improbably, as he shows, by corresponding rather 

 to that of an ancestor of a simpler structure than to its own imago. 

 If we interpret the Professor's phrase " the hind margin " loosely 

 and conversationally as equivalent to the general outline of that 

 portion of the wing, we must agree with his position entirely. It 

 happens, however, that he expressly notes the region outside it as 

 affording nothing to the imaginal structures, and so we must take 

 " hind margin " to mean the actual limit of the wing structure. 



If Poulton's line is not such a limit, what is it? An examination 

 of many pupal wings at various stages of development have satisfied 

 me that it is precisely what it looks like, viz. a vein, of a nature exactly 

 like that of the longitudinal veins that terminate at it. 



Professor Poulton [)oints out that the pupal trachea; at an early 



