The origin and development of the wings of Coleoptera. 547 



The tracheae and tracheoles of the wings of adult Coleoptera 

 are distinct from those of the larva and prepupa. They become 

 functional at pupation, or at the final transformation and remain so 

 throughout the life of the beetle and do not become degenerate as is 

 frequently stated in text books, although they may become flattened 

 and thickened by the deposition of chitin in the lamellae of the 

 elytron or in the intima of the trachea itself. 



6. Formation of the Yeins. 



In the Coleoptera that I have examined the veins appear in the 

 wing before any tracheae enter, a fact also observed by Comstock & 

 Needham in Hymenoptera and thought by them to be true of other 

 insects also. In the younger stages of the wings no traces of veins 

 are found and everywhere the two basement membranes are in close 

 contact (PI. 16, Fig. 21). When the prepupal period is about to 

 begin and the haemolymph begins to be forced anteriorly and enter 

 the foramen of the wing, a system of sinuses in the wing open between 

 the basement membranes. These sinuses which are soon filled with 

 haemolymph and become early visible are the veins in which 

 the tracheae and nerves are retracted in the pupal and adult wing 

 (PI. 16, Figs. 22, 23 and 24). As the prepupal stage progresses 

 and the wing expands, more haemolymph enters, and the veins 

 become great spaces in which the tracheae lie (PI. 16, Fig. 25). 

 The veins are diö'erentely located, even in early stages of the wing 

 where they show the same general arrangement as in the adult 

 structure. The venation of the wings has been ably investigated by 

 Comstock & Needham and I can only confirm their excellent account 

 of the veins in the wings of Coleoptera. I have not found any wings 

 which show traces of the branching of the tracheae as in other insects, 

 and my results confirm their belief that in Coleoptera the tracheation 

 is dependent upon the venation. 



7. Other Tissues in the larTal Wings. 



In addition to the tissues essential to the formation of the wing, 

 hypodermis, haemolymph, and tracheae, other tissue elements or tissues 

 have from time to time been recorded as occurring in insects wings. 



Mesoderm. Very little mesodermal tissue, except haemolymph 

 and leucocytes, is ever found in the wings of beetles.' The leuco- 

 cytes are fairly numerous in the wings but never, as far as I know, 



35* 



