The origin and development of the wings of Coleoptera. 521 



that they originate in the embryonic period. In the Diptera the pre- 

 sense of the imaginai discs in the embryo has been noted by many 

 authors, especially by Pratt (1900), but in the Hymenoptera, Coleo- 

 ptera and the more generalized orders nothing is known of their 

 origin. 



In the Coleoptera the lack of material has made it impossible 

 for me to investigate the embryonic origin of the wing discs as 

 thoroughly as I should wish. Embryonic material of the Chrysomelidae 

 and Coccinellidae is easily obtained, but of the more interesting 

 Cerambycidae and Scarabaeidae I have not been able to secure a 

 sufficient amount for profitable study. Such observations as I have 

 made, fragmentary and unsatisfactory as they are, are, nevertheless, 

 of interest as throwing light upon the condition in the larval stages, 



a) Embryonic Development. 



In the embryo of Leptinotarsa decemlineata, shortly before hatching, 

 or in the newly hatched larva the wing discs will be found lying beneath 

 spots of black pigment on the sides of the last two thoracic segments. 

 In Fig. 19 (PI. 15) are shown the location of these spots and the 

 wing fundament beneath them. 



In the late embryo or young larva the hypodermis is found to be 

 thickened in the area described above, very much in some individuals 

 or scarcely at all in others. There is great variation in this respect; 

 about ten percent showing well developed discs, thirty percent, a slight 

 thickening, and the remainder none that is perceptible. This variation 

 is of considerable interest, and I shall recur to its probable cause 

 further on. In Fig. 14 (PI. 15) is represented a transverse section 

 of a larva about eighteen hours after hatching. This section w^ould, 

 however, show equally well the condition as regards the wing disc in 

 the late embryo. 



The wing disc, or fundament (al fund) lies well up in the pleural 

 region. It is elliptical in surface view and lies between two sets of 

 muscles (mu) which become part of the elevator and depressor muscles 

 of the adult wing. In Fig. 15 (PI. 15) is shown a transverse section 

 of the second abdominal segment from the same larva as Fig. 14. In 

 this section the muscles corresponding to the two seen in Fig. 14 are 

 easily distinguishable, and between them, upon the pleurum, is situated 

 the spiracle. The positions of the wing fundament and of the spiracle 

 are, therefore perfectly homologous. In each section (Figs. 14 and 15, 

 PI. 15) a ventral thickening {dsc. v) is also seen. This occurs regularly 



