The origin and development of the wings of Coleoptera. 533 



3) Enclosed type = Pieris type of Gonin (1894). 



The most complicated method of wing development in beetles is 

 found in the Coccinellidae and Clirysomelidae, and in no other families, 

 as far as is known. Of the two families the former presents a much 

 simpler condition than the latter as regards the wing fundament and 

 its containing sac. 



In both famines the wing fundament is evaginated in the same 

 way. The larger part of the thickened wing disc swings inward from 

 the cuticula as if hinged by the dorsal edge, while a relatively thin 

 layer of hypodermis forms the ventral part of the pocket thus formed. 

 In this type of wing development there is then first a longitudinal 

 furrow above which the hypodermis thickens to form the wing fun- 

 dament and below which it becomes thinner to form the wing sac. 

 By the continued inward movement of the furrow the upper and 

 lower parts of the primitive disc are made to behave as described 

 above. The lips of the pocket now come together forming a closed sac 

 which completely cuts off the wing fundament from the outside world 

 (PI. 15, Fig. 18). In the Coccinellid, H. ISpundata, CoiMSTOCk & 

 Needham (1899) describe and figure the wing sacs as open structures 

 much like those found in the Scarahaeidae. They state that "as 

 growth continues, the wing extends itself slowly ventrally, as shown 

 in fig. 86; the mouth of its enveloping pouch becomes somewhat 

 closed by the growth and extension of the pleural hypodermis, but 

 to various degrees, in different specimens, a larger part of the 

 larval wing being often found covered exteriorly only by the chitin 

 of the integument." I have been unable to corroborate their observ- 

 ations with properly preserved material. Specimens killed in Hermann's 

 or Flemming's fluid or sublimate acetic acid mixtures do not show 

 this structure, as the edges of the wing pocket being in close contact, close 

 the wing sac (PI. 20, Figs. 65 and 66). With material killed in Peeenyi's 

 fluid, picric acid mixtures, hot water, or alcohol and corrosive sub- 

 limate exactly the conditions described by Comstock & Needham are 

 found ; and this is due to the great shrinkage and distortion produced 

 by these reagents upon insect tissue. 



In L. decemlineata, after the invagination of the hypodermis the 

 opening of the wing pocket closes, but the lips do not fuse for more 

 than the posterior half of the opening. A closed sac is thus formed 

 with the dorsal wall thick, the ventral wall thin. The dorsal part 

 now evaginates downward into the wing sac, and soon the growing 

 wing has obliterated the cavity of the invagination, so that the dorsal 



