MOEPHOLOGT OP THE LEPIDOPTEROUS PUPA. 189 



pupal period the formation of irnaginal appendages within those of the pupa is deferred 

 until very late, and then takes place rapidly in the lapse of a few weeks. This also 

 strengthens the conclusion that such pupal appendages are not mere cases for the parts 

 of the imago, inasmuch as these latter are only contained within them for a very small 

 proportion of the wdiole pupal period. 



A Classification of the various Features constituting the External Morphology of the 

 Pupa. — Anticipating the results of investigations to be described in future papers, we 

 shall find that the features which can be made out on the surface of a pupa may be 

 grouped, according to their origin, under four chief heads : — 



I. The first of these heads includes the essential and ancestral features derived from 

 stages of a more ancient and continuous form of metamorphosis, and probably in some 

 cases also transmitted from the ultimate, sexually mature, stage of a still earlier and 

 simpler method of development. To this division belongs the general structure of the 

 body : its segments, spiracles, limbs, wings, and probably antennae ; but not the details 

 of these. Also, more specially, the pupal external generative organs and the crescent- 

 shaped compound eye. 



II. The second head includes those modifications of the general structure which are 

 due to the development of a very different form within it. These modifications have 

 determined the special form and, in some cases, sculpture of the wings, limbs, and 

 antennae, and have probably taken a much larger share in producing the present form of 

 the pupal maxillae. Inasmuch as a modification once wrought upon the pupa will often 

 outlive the imaginal structure which caused it, we have some interesting proofs of former 

 structural arrangements in the imago. These modifications due to the imago may be 

 classified : (a) Those details which are common to a large number of pupae, and in which 

 the imaginal structures fit the corresponding parts of the pupa. This includes the vast 

 majority of the details arranged under the second head. (j3) Those obviously recent 

 and exceptional modifications of the pupal structure which have been formed to accom- 

 modate a rapidly increasing imaginal structure. This includes the development of special 

 outgrowths to contain the elongating imaginal maxillae, (-y) Those details which, once 

 impressed by an imaginal structure, have remained after the latter has shrunk and 

 changed. This includes the large pectinated antennae of female pupa?, giving rise to 

 imagines with filiform antennae. (<$) Those details which have followed the collapse of 

 the contained imaginal structure, but have kept behind the latter, so that they form 

 actual proofs of the shrinkage by showing to us that the imaginal structures were once 

 a size larger. This includes the wdngs of female pupae without the power of flight in 

 the imago stage. 



III. The third head includes those structures or marks which are due to the adult larva, 

 and are of no morphological significance. These are either a mere concession to the 

 mechanical condition of the process of pupation (scars of claspers and processes) or are 

 due to the larval pigment still lingering unchanged in the pupal hypodermis cells. 



IV. The fourth head includes those features which are due to the exigencies of pupal 

 life as it now is. Such are the protective forms, markings, and colours of exposed pupae ; 

 the colour of those that pupate in or upon the earth ; and the rings of locomotive hooks 



29* 



