﻿112 CLEMENS' SYNOPSIS OF 



The legs too, are passive during the process, and are folded on the thorax ; at least 

 this applies to the anterior, but the posterior pair may aid the extruding efforts of the 

 thorax, particularly in those species whose transformation is subterranean, and this is 

 probably one of the principal objects of the tibial spurs. The wings are thrown over 

 the back, and the force of the efforts falling chiefly on the under surface of the base of 

 their attachment, the principal veins will always be found denuded. The action of the 

 thoracic muscles is so powerful and effectual, that a few moments suffice to complete 

 the process of insect parturition. After the extraction of the thorax, the feet are 

 called into play to aid in the delivery of the abdomen, which is extracted chiefly by 

 means of a curious vermicular motion. 



After parturition has been effected, the dilatation and expansion of the wings them- 

 selves take place, and during which there is a positive increase in size, or a gradual 

 extension of their structure. At this period an excised wing is very easily dissected ; 

 or the same thing can be accomplished in the dried wing after prolonged maceration 

 in water, to which a very small quantity of hydrochloric acid has been added. Thus 

 we ascertain, that the wing consists of two distinct portions, which are capa,ble of 

 being separated from each other. One of these consists of an extremely delicate 

 double membrane, one on the upper and one on the lower surface, and which are in- 

 deed essentially the same, being continuous at their edges, spread over a system of 

 prolongations of the chitinic substance of the external skeleton, assuming here the 

 form of tubes. These constitute the neuration of the wings, or the pterogostic struc- 

 ture which fulfils two purposes. In the first place, they confer the necessary light- 

 ness on the wings, and at the same time the strength to resist vibrations on the 

 atmosphere, and also protect the ramifications of the tracheal system. These chitinic 

 tubes also afford channels, in which the early circulation of the nutritive fluids or 

 blood, is conducted through the wings during their expansion ; for, at this period it is 

 very active, but almost entirely disappears subsequently, especially in those whose 

 lives are short. This circulating fluid, at this time, is true blood, containing a large 

 number of black granules, although perfectly homogeneous at first, and forms a de- 

 cided clot. 



The rudiments of these tubes may be traced in the forming wings in the larva, 

 just previous to transformation, by the distribution of the principal tracheal trunks of 

 these forming organs, and still more distinctly in the pupa. No nutritive process 

 takes place in the wings, in all probability, after they have attained their full develop- 

 ment, and have hardened, and the terminal ends of the tubes being open, just 

 sufficient circulation is maintained in them to confer the necessary degree of pliancy. 

 In the act of wing expansion, these tubes undergo a positive elongation, and a separa- 

 tion of the branches takes place, so that the membranes of the wing are stretched, 

 not only longitudinally, but transversely. From this fact, and because if one-half the 



