70 BEITISH LEPIDOPTERA. 



in the quiescent stage preceding pupation, whilst the final growth and 

 final histolytic processes that complete the imaginal growth alone take 

 place in the pupal stage. 



The antennae of the imago bear the same relation to those of the 

 larva as the imaginal bears to the larval leg. The larval organ is only 

 the point of departure of the imaginal development. Weismann has 

 shown how, in Corethra, at the approach of each moult, an invagina- 

 tion like the finger of a glove allows the antenna to become elongated 

 from its base. The process is identical in the larva of Pieris. At the 

 last moult the invagination is so pronounced that it is not effaced with 

 the renewal of the chitinous skeleton. Some days later it commences 

 to enlarge. As the bud sinks into the head cavity it forces back the 

 hypodermal wall, and makes of it an envelope for itself. Its base, 

 widely open, allows the entrance of the nerves, capillaries, and a large 

 trachea. As soon as it reaches the posterior region of the head, the 

 antennas, in order to become still more elongated, become strongly 

 folded, and describe large curves (compared by Keaumur with a ram's 

 horn). The membranous envelope thickens inwardly and around the 

 base of the organ. Its subsequent behaviour is connected with that of 

 two other hypodermic structures. It is, in the first place, entirely a 

 base for the cells which, in the larva, carry the ocelli. This base, 

 hidden on each side beneath the parietal wall, is thickened and 

 regenerated, whilst a circular pad or cushion gives it the outline and 

 the form of the imaginal eye. Lastly, we have a conical prolongation, 

 surmounting the head, which presents, at emergence, a tuft of long 

 hairs, to which Gronin has given the name of " cimier." It is charac- 

 teristic of the Pierid pupa3. It is only differentiated towards the end 

 of the 4th larval stadium in a median depression of the head, and is an 

 imaginal disc in the widest sense of the term. On each side the base 

 of the antenna comes in contact with the germ of the " cimier." The 

 envelopes approach, and their thickened part constitutes, with the 

 ocellar discs, a new cephalic wall. The imaginal head, thus bounded, 

 is triangular, and all the larval structures remaining outside this area 

 have to disappear. The muscles and the nerves are resolved by 

 histolysis, then the external part of the imaginal envelope and the old 

 hypoderm wall, thinned out and degenerated, becomes detached in 

 shreds. The antenna then becomes external throughout its whole 

 extent. Consequently, the transformation is almost as complete here, 

 in Pieris, as in the thorax of the Diptera or Hymenoptera. It is neces- 

 sitated by the change of form and of volume cf the head. The ocellar 

 region persists almost alone from the larva to the imago. As for the 

 rest, the limit is not very exact between that which is replaced by sub- 

 stitution or that by direct renewal from the epithelium. 



The development of the trunk or maxillae is so similar to that of the 

 antennas that it is scarcely necessary to give a special description. Start- 

 ing from the last moult, the hypodermic contents of the maxilla? draw 

 back into the cephalic cavity in the form of a hollow bud, of which the 

 base is turned internally. The invagination remains less accentuated than 

 around the antennas. It does not even extend to the anterior part of the 

 oesophagus. The two symmetrical halves of the maxilla? approach and 

 become folded Avhen the larva ceases feeding, each of these incurves in 

 the form of an S, and remains entirely lodged under the floor of the 

 mouth. Two other buds are seen beneath those that give rise to the 



