570 Dr. Thomas Algernon Chapman on the 



acquirement of active pupal jaws, and that the discovery 

 thus made that an imago without jaws was a satisfactory 

 organism, opened up the whole field for the evolution both 

 of the Le2ndoj)tera and Uiptera. I may say that I see 

 every reason to believe that the Diptera also originated 

 here, along with the Lepidopfera, and that they had to 

 face the same problems that beset the Lepidoptera as to 

 the escape of the imago from its cocoon, without the use 

 of imaginal jaws. Up to a certain point their solutions 

 were very similar, but later the Diptera made one or two 

 remarkable advances, of which we find no trace in the 

 Lepidoptera. 



The history of the evolution of the Lepidoptera, from a 

 pupal point of view, is, then, from the very beginning, a 

 history of the solution in various ways and degrees, of the 

 problem of how to escape from the cocoon without the aid 

 of imaginal jaws ; if this was not the dominant feature in 

 lepidopterous evolution, it was at least so important as 

 to leave distinctive features on almost every family of 

 Lepidoptera, up to the point at which the problem appears 

 to have received the most satisfactory possible solution, 

 or rather a most satisfactory possible solution. When 

 this point was reached, and it appears to have been 

 reached by several different roads, their pupal structure 

 presents a great similarity amongst a large number of very 

 distinct and unallied families — those, in fact, which are 

 classed together as Macro-hcterocera. 



Taking, then, the Micropteri/ges as being the lowest 

 Lepidoptera from our present as from most other points of 

 view, we find a method of escape from the cocoon that 

 differs in several important respects from that in which the 

 perfect imago accomplishes this by the aid of its own jaws. 



We may note, however, that though it is nominally the 

 pupa that escapes from the cocoon, it is in reality still the 

 imago, the imago clothed in the effete pupal skin. To 

 rupture the cocoon, it uses not its own jaws, but those of 

 the pupal skin, energising them, however, in some totally 

 different way from ordinary direct muscular action, their 

 movements being the result of the vermicular movements 

 of the pupa, acting probably by fluid pressure on the 

 articular structure of the jaws, by some arrangement not 

 altogether different perhaps from the frontal sac of the 

 higher Diptera. 



How this extraordinary method of escape originated 



