158 BRUES. [VOL. I. 



joints of the tarsus. The wall of the trachea lies closely 

 applied to the exoskeleton of the metatarsus, except for a very 

 short distance on one side of the leg, where it is semicircu- 

 larly bent inward to leave space for the claw tendon which lies 

 in the tubular space thus formed (Fig. 5). Here as in the tibia 

 the taenidia are visible on only about one-fifteenth of the cir- 

 cumference on each side. 



The walls of the trachea are here not entirely destitute of 

 taenidia, as is the case with the air vesicles which appear in the 

 body cavities of many active insects. The striations have re- 

 mained on that part of the tracheal wall which encloses the 

 tendon (Fig. 4). At the point where the tendon passes, the 

 taenidia are thickened and quite robust, but on each side they 

 gradually become weak and fade out entirely. An exactly 

 symmetrical formation of the taenidia is present on the side 

 opposite to the tendon. It is evident that the thickenings on 

 the tendon side may have been retained in order to strengthen 

 the tube at this point, but there is apparently no reason for the 

 anomalous thickening on the opposide side. In the second 

 and third joints the taenidia lengthen until they extend over 

 one-seventh of the circumference. The trachea seems to stop 

 suddenly here, as I have been unable to trace it further. 



There are few insects presenting similar enlargements of the 

 leg joints, if we except those forms such as jumping OrtJioptera 

 and Chrysomelidae, where the increase in size is evidently for 

 the accommodation of the larger muscles. Graber and Lub- 

 bock mention enlargements of the trachea in the tibiae of 

 OrtJioptera, ants and Termitidae, serving as auditory or chor- 

 dotonal organs. In this case the adaptation is very extraor- 

 dinary, but the dilatation of the trachea is not comparable to 

 that of Bittacomorpha in extent. Bittacomorpha presents the 

 only case known to me of a considerable tracheal dilatation 

 occurring in the insect leg. In the males of many Empididac, 

 and notably species of Hilara, e.g., Hilara trivittata Lw., the 

 metatarsus of the front leg is greatly enlarged (Fig. 7), but here 

 the cavity is occupied in great part by muscular tissue, the 

 trachea being very slender (Fig. 8). In this species there 

 seems to be no trachea beyond the end of the metatarsus. 



