156 BRUES. [VOL. I. 



gated breathing tube, produced by the excessive lengthening of 

 the posterior end of the abdomen (Fig. i). This formation is 

 not peculiar to this species, as it occurs elsewhere, even in 

 insects in nowise related, as in Eristalis among the Syrpltidae. 

 In the pupa we find a respiratory tube present, but in this 

 instar its insertion is exactly reversed ; it proceeds from the 

 head. Although only one tube is functionally developed, it is 

 one of a pair which has lengthened at the expense of its fel- 

 low (Fig. 2). Moreover, it is not always the same tube which 

 is developed. Hart mentions that twenty-seven pupae had the 

 right tube elongated as against three in which the left tube 

 functioned. In one anomalous case both were developed, but 

 unequally, their combined length being equal to that of the 

 long one in normal pupae. This unequal length of the tubes 

 is characteristic also of Ptychoptera. 



Up to the present time it has not been known that the 

 imago also possesses a remarkable modification of the tracheal 

 system. In this stage, however, it is to be found in the legs. 



In both sexes the metatarsi are very much enlarged and 

 quite conspicuous on account of their great color contrast. 

 The second and third tarsal joints are also somewhat enlarged, 

 but not nearly to so great an extent. 



In order to study the tracheal system of the legs they were 

 decolorized in chlorine water and mounted whole or split into 

 halves. Some specimens were treated also with potassium 

 hydroxide, which successfully separated the delicate tracheae 

 from the integument. Legs were also sectioned in paraffin to 

 show the disposition of the internal parts. 



In the basal part of the legs the tracheal tube is of the ordi- 

 nary form and size. It begins to enlarge just before the mid- 

 dle of the femur, and before it has reached the tip is equal to 

 seven-eighths the diameter of the femur. At this point the 

 taenidia extend entirely around the tube, although faint in 

 some places. The whole tibia is completely filled up by the 

 trachea, which is striated on each side for only about one- 

 fifteenth of its circumference. In the enlarged metatarsus the 

 trachea is enormously distended and almost completely fills the 

 cavity of this joint as well as that of the second and third 



