THE EXTERNAL MORPHOLOGY OF THE LEPIDOPTEROUS PUPA. 39 



incisions. Some difficulty is experienced in homologising some of the 

 appendages of the obtect pupa in which the cephalic appendages are 

 soldered together. We know of no example of a coarctate pupa among 

 the Lepidoptera. Such are enclosed in the old larval skin which 

 forms a pupal covering, and are particularly well-developed in some 

 Diptera. 



The assumption of the pupal stage (as also the appearance of the 

 imago) is the concomitant of an ecdysis, and really commences with 

 the quiescent larval stage that precedes the actual taking on of the 

 pupal form. The pupa can be dissected out of the skin of a mature 

 larva many hours before the occurrence of normal pupation, and under 

 these conditions the limbs are not soldered down by the secretion that 

 afterwards encloses the pupa and fixes the appendages in the pupas- 

 obtectaa. This fact has led to many authors erroneously describing 

 the wings, legs, &c, as appendages of the imago, and not as pupal 

 structures, a view that has to be corrected before one can arrive at a 

 logical conception of the true nature of the pupal form in holometa- 

 bolous insects. Chapman points out, with regard to this, that, if an 

 empty case of a pupa-incompleta (Oossus, Sesia, &c.) be examined, the 

 cover of any appendage is found to be nearly perfect, e.f/., the antenna- 

 case is observed to be a tube with an opening on the inner surface 

 close up to the head, through which the antenna has been withdrawn ; 

 in a pupa-obtecta it is a plate only, the inner side of the tube may or 

 may not present just a discoverable shred of membrane. Evidently 

 evolution has proceeded further in this direction in the obtect than in 

 the incomplete pupa. 



The pupa then must be considered per se, not as an extension of 

 the larval state, nor as a mere preliminary to the imaginal, but as an 

 independent stage with organs and functions peculiarly its own. It is 

 evident, therefore, that it is erroneous to speak of the various parts of 

 the pupa, as if they were merely cases for the corresponding parts of 

 the imago, and Poulton observes that the terms ophthalmotheca?, 

 pterothecae, ceratothecae, podothecaa, &c, which have been applied to 

 the parts within which the imaginal eyes, wings, antennaa, legs, &c, 

 are developed, tend to obscure the true nature of the pupal organs 

 which are more correctly described as pupal eyes, wings, antennaa, and 

 legs, and it may be here noted that, although the imaginal organs may 

 be formed within the corresponding pupal ones, the form and structure 

 of the latter are different from, and, according to Poulton, are often 

 far more ancestral than, those of the former. They are, he says, 

 " remnants of a time when the last stage of metamorphosis in the 

 ancestors of Lepidoptera was something very different from a butterfly 

 or moth. The old terminology obscured the fact that the pupa has a 

 morphological meaning of its own, and that traces of an exceedingly 

 remote past can be deciphered by the study of its structure." Sharp 

 points out (Insects, p. 169) that " although the existence of a pupa is 

 to the eye the most striking difference between insects with perfect and 

 those with imperfect metamorphosis, yet there is reason for supposing 

 that the pupa and the pupal period are really of less importance than 

 at first sight they appear to be. The condition that precedes the 

 appearance of the pupa is really the period of the most important 

 change," &c. Poulton further notes that Weismann's great discovery 

 of the theory of histolysis, by which certain of the tissues break down 



