48 THE TRACHEATION OF WINGS 



The jumping Orthoptera (Fig. 33) have the tracheation of the hind leg 

 greatly modified in that a part of the tracheae come from the second 

 abdominal spiracle. This is a condition which has been met with nowhere 

 else and is undoubtedly due to the great development of the hind leg and its 

 intrtision into the abdominal region. 



THE COMPARATIVE VALUES OF THE AIR SUPPLIES TO THE TWO PRINCIPAL 

 TRACHEAE OF THE WINGS 



The value of the air supply of the wing tracheae has been suspected of 

 being the cause of some of the tracheal modifications of the wings. This 

 theorv^ has been mentioned in the introduction of this paper and it has been 

 given some study by Tillyard (1. c. p. 207-218). This author has made a 

 study of the Odonata where the basal connections of the tracheae are most 

 highly modified. The author has formulated a theory, as the result of his 

 work, which reads as follows: 



"The peculiarities shown by the wing-venation of the Odonata, as con- 

 trasted with that of other insects, are due primarily to the aquatic habits of 

 the larvae; whereby, thru the development of rectal or caudal breathing, 

 the oxygen-supply of the developing wing is carried from the posterior end 

 of the body, and enters the wing-base at its anal end." 



The invasion of the area of the radial sector by the medial trachea is 

 accounted for by the fact that the medial trachea is nearer the air supply 

 than the radial trachea. Several other modifications are ascribed to the 

 same cause. 



The Odonata would seem a very unfavorable order to use in the study 

 of the comparative values of the air supplies to the wings because the 

 conditions are so highly specialized. A better understanding of the subject 

 may be had by returning to the typical condition of the tracheal connec- 

 tions and following the various lines of development. 



Each wing typically receives air from two spiracles and the meta- 

 thoracic spiracle (Fig. 17, spi) supplies the cubito-anal portion of the front 

 wing and the costo-radial portion of the hind wing. It may be assumed 

 that the three typical sources of air supply are equal. The Lepidoptera 

 (Fig. 21) have the tracheal connections to the wings very generalized but the 

 metathoracic spiracle (r. sp) is rudimentary in the pupa. This would 

 seem to make the air supply to the cubito-anal portion of the front wing 

 and the costo-radial portion of the hind wing inferior to the others and the 

 tracheation of the two wings should be quite different. On the other hand 

 the tracheae seem to have been unmodified and to have retained their 

 typical relationships. 



It is difficult to apply the air-supply theory to the case of the honey-bee 

 for the hind wing has lost its cubito-anal connection which was with the 

 functional first abdominal spiracle (Fig. 32 spz) and has retained its costo- 



