232 EEMAEKABLE STRUCTUEE IN 



I have therefore been very much interested by dis- 

 covering (1875) in ants a structure which seems in 

 some remarkable points to resemble that of the 

 Orthoptera. As will be seen from a glance at Dr. 

 Graber's memoir, and the plates which accompany it, 

 the large trachea of the leg in the Orthoptera is con- 

 siderably swollen in the tibia, and sends off, shortly 

 after entering the tibia, a branch which, after running 

 for some time parallel to the principal trunk, joins it 

 again. See, for instance, in his monograph, plate ii., 

 fig. 43 ; plate vi., fig. 69 ; plate vii., fig. 77 ; &c. 



Now, I have observed that in many other insects the 

 tracheae of the tibia are dilated, and in several I have 

 been able to detect a recurrent branch. The same ig 

 also the case in some mites. I will, however, reserve 

 what I have to say on this subject, with reference to 

 other insects, for another occasion, and will at present 

 confine myself to the ants. If we examine the tibia, 

 say of Lasius fiavus. Fig. 9, we shall see that the 

 trachea presents a remarkable arrangement, which at 

 once reminds us of that which occurs in Gryllus and 

 other Orthoptera. In the femur it has a diameter of 

 about -3-^oT ^^ ^^ ^^^^ » ^^ soon, however, as it entei's 

 the tibia, it swells to a diameter of about g-J-^ of an 

 inch, then contracts again to g-i-^, and then again, at 

 the apical extremity of the tibia, once more expands 

 to 5-J3. Moreover, as in Gryllus, so also in Formica, a 

 small branch rises from the upper sac, runs almost 



