16 Journal New York Entomological Society. [\oi. vin. 



ends of the hyi^odermal cells. This membrane is easily seen in the 

 early larval stages to be continuous with the basement membrane of 

 the hypodermis of the body wall and is obviously a homologous struc- 

 ture. In the fourth larval stage, tlie upper and lower hypodermal lay- 

 ers of the bud come together and the two opposed basement mem- 

 branes appear as a single membrane : this has been termed the middle 

 moiihraih- of the larval wings, and its homology with the two base- 

 ment membranes of the u])])er and the lower hypodermal layers of the 

 wing overlooked. At the end of the fifth larval stage just before the 

 evagination of the wings, which is characteristic of the prepupal 

 period, the wing-buds become transparent so that they are seen in dis- 

 section with difficulty ; tFieir position, as already indicated, is rec- 

 ognizable only by the accompanying trachCcV. In sections of the 

 wing-buds made at this time, the so-called middle membrane is seen 

 only with difficulty. This has given rise to the belief that it disap- 

 pears at this time. Later when the wings become more opacpie, /. c, 

 in the pupa stage, the two basement membranes are again easily seen. 

 Semper ('57 ) believed that the reappearing basement membrane was 

 a new structure, which he named the,v;v///r//;/f7;//v(?// ; and he describes 

 its formation from mesenchymatous cells that had wandered into the 

 wing. The result has been that students of the subject have been 

 confused by descriptions of three different structures, the Ijasement 

 membrane of the hypodermis, the middle membrane of the larval 

 wing-buds, and the grundmemljran of the pupal wing ; when in real- 

 ity there is only a single structure, the basement membrane. 



The Developmeuf of the Venatuui of the Jl7//xs- — As stated above, 

 during the fourth larval stage, the upper and lower hypodermal layers 

 of the wing-bud come together, and the two opposed basement mem- 

 branes appear as a single membrane, the so-called middle membrane. 

 This union of the two layers of the wing does not take place, how- 

 ever, throughout the entire extent of the bud. Along certain lines, 

 spaces occupied by tracheoles and lymph remain. These are thefore- 

 runfiers of vein cavities, and into these the tracheix; extend during the 

 fifth stage (Fig. 12). In the fifth stage, therefore, the \'enation of 

 the wing is outlined, each vein consisting of a cavity filled with lymph 

 and containing a trachea. It is not, however, till the pupa stage that 

 the wing-veins in the same sense in which the term is used by Ento- 

 mologists (/. e., the cuticular framework of the wing) are developed. 

 These so-called wing-veins are merely thickened lines of the cuticle 

 bounding the pre-existing vein-cavities. 



