The origin and development of the wings of Coleoptera. 555 



cytoplasm. These paired groups of cells are arranged in rows 

 {L. decemlineata), irregularly (0. scahra), or in a complex pattern 

 {Chrysomela and Calligrapha). During the pupal stage and until after 

 the wing is completely expanded these groups of cells remain inactive. 

 Wherever they occur the basement membrane of the dorsal and 

 ventral layer of hypodermis passes across the middle space of the 

 wing, forming a tube which puts the two subhypodermal spaces in 

 connection, as in the Lepidoptera. 



In the young adult after the wing has become fully expanded 

 the cells at the upper side begin to secrete chitiu and form a conical 

 projection on the underside of the cuticula reaching down into a cone- 

 shaped pocket of hypodermis (PI. 20, Fig. 78). This secretion of chitin 

 continues, the chitinous process growing deeper and deeper into the 

 wing, and at the same time the cells of the dorsal layer of hypodermis 

 have migrated down the sides of this process and completely covered it. 

 The original half dozen cells which started the process have had their 

 numbers increased by additions from the neighbouring hypodermis. 

 Eventually, the column reaches the ventral layer of the wing and 

 fuses with it, thus forming a solid chitinous column connecting the 

 two sides of the elytron and giving it great rigidity. In almost all 

 beetles a small pit is formed above these columns which is due to 

 the contraction on the part of the hypodermal cells of the ventral 

 layer pulling the cells of the dorsal layer down and bringing the soft 

 primary cuticula with them (PI. 20, Fig. 79). 



After the column is fully formed the deposition of chitin may 

 cease for a short time until the pigmentation of the primary cuticula 

 is completed and then all of the cells of the hypodermis begin de- 

 positing chitin of another kind, the secondary cuticula, which forms 

 the backing and strength of the wing. Eventually, the column 

 becomes a strong structure occupying a considerable space in the 

 wing. 



The fully developed column (PI. 20, Fig. 79) consists of a 

 central rod which is continuous with the primary cuticula of both 

 sides of the wing, surrounded by another layer of the secondary cuti- 

 cula which varies much in thickness even in the same wing and also 

 with age. This secondary cuticula is longitudinally stratified and 

 has numerous delicate pore canals running transversely to the line of 

 stratification. These pore canals penetrate as far outward as the 

 primary cuticula, and are occupied during growth by fine processes from 



