658 TEXT-BOOK OF ENTOMOLOGY 



by Gonin the crest (cimier, Fig. 612), which is characteristic of 

 the pupae of Pieridse. It is only differentiated towards the end 

 of the 4th larval stage in a median depression of the vertex. It is 



an imaginal bud in the 

 a f most general sense of the 



word. 



m On each side the base of 



..... jo the antenna comes in con- 

 tact with the germ of the 

 crest - The envelopes ap- 

 a proach each other, and their 

 thickened part constitutes 

 with the ocular disks a new 

 cephalic wall. The head of 



FIG. 613. Larva of Pier-is brassicce stripped of its ^ Vmtfpvflv fhn<s 

 skin some minutes before pupation : the antenme (</) have il j 



been displaced, and the tongue cut off, to show the palpi fp fv^nno-nloi- all 



(p); c, cimier; o, eye; m, vestige of a mandible ; t, inser- ridllgUlell , 



tion of the tongue (see Fig. 612); au, fore, up, hind, wings; l avva l riqvfs vpmainin"- Ollt 

 g, knee of a foot of the 3d pair. 



of this area then disappear. 



The muscles and the nerves are resorbed by histolysis, then the 

 external part of the imaginal envelopes and the old parietal hypo- 

 dermis, reduced very thin and degenerated, is detached in shreds. 

 The antenna becomes external throughout its whole extent. The 

 transformation is in this case, then, almost as complete as in the 

 thorax of Diptera or Hymenoptera. It is necessitated by the change 

 of form and of volume of the head. The region of the ocelli per- 

 sists unchanged almost alone from the larva to the imago also. The 

 limit is not well marked between the portion which is the replace- 

 ment or direct renovation of the epithelium. 



Maxilla and labial palpi. --The development of the tongue (1st 

 maxillae) is so like that of the antennae that it scarcely needs descrip- 

 tion. Beginning at the last moult, the hypodermic contents of the 

 maxillae is withdrawn in the cephalic cavity under the form of a 

 hollow bud whose base is turned inward. The invagination remains 

 less distinct than in the antennas; it does not even reach to the 

 anterior part of the oesophagus. The two symmetrical halves of the 

 tongue approach each other and are thrice folded. AVhen the outer- 

 pillar stops feeding, they each curve in in the form of an S, remain- 

 ing lodged under the floor of the mouth (Fig. 613, ). 



Underneath are to be seen two other buds, which by an identical 

 process become the labial palpi (Figs. 614, 615, />) 



At the anterior part of the head, where the organs are very close 

 together, the envelopes form several folds without any further use 



