The origin and development of the wings of Coleoptera. 551 



toughened and are able to hold the two sides of the wing in contact 

 ■when the imago emerges and the wing expands. 



To facilitate ecdysis at pupation many beetle larvae develop 

 "deciduous spines" upon the elytra, prothorax and other i)arts of the 

 body. These spines are of quite general occurrence in insects, in the 

 Coleoptera reaching a high state of development in the Coc- 

 cinellidae. In Epilaclma horealis these spines are most extravagantly 

 developed, each elytron having at pupation its shoulder and two 

 longitudinal spaces thickly beset with long, cylindrical, spines or 

 scales. Similar structures also occur upon the head, pronotum and 

 abdomen. In development these spines follow the same general plan 

 as that given by Mater (1896) for the scales of Lepidoptera. 



The first indication of these structures is found when the larva 

 is about two thirds grown. Certain hypodermal cells are found 

 to be enlarging rapidly so that they soon become flask shaped like 

 the "matrix cells" of Mayer (1896), but they remain attached to the 

 basement membrane of the wing (PI. 18, Fig. 40). These cells have 

 a large nucleus and dense granular cytoplasm, with one or two 

 deeply stained bodies in the cytoplasm close to the nucleus. Most 

 of the cells at this stage have already developed a short pro- 

 jection above the general level of the hypodermis, but no further 

 development takes place until the prepupal stage. Early in the pre- 

 pupal stage, soon after the wings become external structures, these 

 cells develop long cylindrical prolongations, which cause a decrease 

 in the volume of the matrix cells and a migration of the densely 

 stained granule to a position at the base of the scale (PI. 18, Fig. 41). 

 Just before pupation the scales develop a thick chitinous covering 

 which makes them rigid and effective in raising the old cuticula from 

 the surface of the insect, and allowing the pupa to slide out of its 

 old chitinous coat with ease (PI, 18, Fig. 42). These spines are 

 present in the pupa, where they become hard and blackened and per- 

 haps serve as protective structures, but they are lost at the final trans- 

 formation and no trace of them occurs in the adult. 



Early in the prepupal stage the exuvial fluid begins to collect 

 about the rapidly growing wings so that during this period they are 

 really suspended in a watery fluid which is secreted by special glands, 

 the behavior of which I have described in another place. 



At pupation the exuvial fluid is so abundant that the developing 

 pupa is immersed in it inside of the old larval skin. Finally this is 

 ruptured, and the air entering, the exuvial fluid is in i)art precipitated 

 upon the surface of the pupa. As ecdysis progresses, contact with 



