38 THE VOYAGE OF H.M.S. CHALLENGER. 



Tlie Hind Legs. 



In ofeneral form these resemble the middle legs, but are somewhat shorter and less 

 stout. 



The Acetahulum has been already described. 



The Coxa is three or more times as long as broad, slightly curved outwards, and 

 slightly incrassate at the apex. 



The Trochanter is shorter and thinner than the middle trochanter. 

 - TJie Feimtr shorter and thinner than the middle femur. 



Tlie Tibia has not the frincre of hairs on the inner side. 



The Tarsus (PL III. figs. 18 and 19) is one-jointed. The joint is similar to the second 

 joint of the middle legs, but has not the fringe of hairs on the inner side, and the excava- 

 tion for the claws is rather more distant from the tip. Like the middle tarsus there is, on 

 the side of the joint opposite to the claws, one to three long hairs inserted at different 

 places, and reaching to or beyond the apex of the joint. The ribbon-like process from 

 between the claws is also present. The claws measure in iviiUerstorffi about "15 mm., and 

 in sericeus '12 mm. 



Eespiratoey System. 



As in most other insects, air is admitted to the tracheal system by means of spiracles. 

 I have failed to find any trace of prothoracic spiracles. The large mesothoracic spiracles 

 have already been noticed (p. 30). The remaining spiracles are nearly circular in outline, 

 and the first pair of these are inserted near the posterior end of the thorax (though 

 possibly abdominal), and more or less near the sides of the body is one i^air, and in the 

 abdomen six pairs can without much difficulty be made out ; and possibly others may 

 exist, but may be concealed by the legs. Those that can be seen are as follows : — One pair 

 on the first segment, usually covered by the thorax ; one pair on each of the last three 

 segments situated nearer the side of the body than those on the first segment ; one pair 

 on the first genital segment ; and one pair on the second genital segment, situated at the 

 posterior angles in the male, and about the middle of the side in the female. Measurements 

 of the various circular spiracles give an average of, in willlerstorffi, "035, and in sericeus, 

 "025 mm. for the long diametei". 



In the last two segments of the larva no spiracles exist. 



I regret very much that w'aut of material has prevented me from examining the 

 internal anatomy more completely. 



