The origin and development of the wings of Coleoptera. 557 



Straight sinuses between the basement membranes. Soon, however, 

 the membranes, after reaching the adult stage, draw apart, opening 

 up the whole primitive invagination cavity, so that the position of 

 the veins can now be recognized only by the location and course of 

 the tracheae, which are kept in position by the small branches rami- 

 fying from the main trunks into the tissues of the elytron. 



6) Glands. The glands of the elytra are numerous, both simple 

 and compound glands being found in varying degrees of complexity. 

 The glandular structures of the elytra of beetles have been studied by 

 Hoffbauer (1892) who found both simple and compound glands in 

 the elytra and also upon the head and pronotum. 



The simplest glands are single hypodermal cells modified for a 

 glandular function, and are uniformly distributed over the entire 

 body surface. In the elytron they arise in the pupal stage by the 

 direct modification of one of the hypodermal cells of the wing lamella. 

 In the formation of one of these glands the body of the hypodermal 

 cells drops below the level of the rest, and becomes larger, with a more 

 densely granular cytoplasm and a large round nucleus having a deeply 

 staining chromatin skein (PI. 18, Fig. 37). As the pupal stage progresses 

 the body of the cell becomes larger, the basal connection with the 

 basement membrane becomes extremely attenuated or may be lost 

 entirely, and the cytoplasm becomes filled with globules of secreted 

 material (PI. 18, Fig. 38), which eventually form large vacuoles (PL 18, 

 Fig. 39). At the final ecdysis the end of the cell is laid bare and 

 a minute pore is developed through which the secreted contents of 

 the cell escape to the surface. 



A more complicated gland is shown in Fig. 47 (PI. 18) where 

 several of these simple glands open through a series of tubes into a 

 pit on the surface of the cuticula. The individual cells of the gland 

 undergo the same series of changes in development as do the simple 

 glands. These groups of simple glands are usually arranged in rows 

 in the intertracheal spaces. Often instead of opening at the bottom 

 of a pit (PI. 18, Fig. 40) they open at the top of a cone or stalk 

 situated in a pit (PI. 20, Fig. 68). From the relatively simple 

 aggregation of gland cells shown in Figs. 40 and 68 all gradations 

 are found leading up to the complex structure shown in Fig. 80 

 (PI. 20). This latter structure occurs in regular intertracheal rows 

 on the elytra (PI. 17, Fig. 36) and also upon the head and pronotum 

 of L. decemlineata. This last gland arises as an invagination of a 



