148 SIR JOHN LUBBOCK ON THE ANATOMY OF ANTS. 



I have therefore been very much interested by discovering 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 is considerably 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, pi. ii. fig. 43, pi. vi. fig. 09, pi. vii. 

 fig. 77, &c. Now I have observed that in many other insects the tracheae of the tibia 

 are dilated, sometimes with a recurrent branch. The same is the case even 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 Jlaviis, we shall see that the trachea presents a remark- 

 able 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<fo5 °f an mcn > as soon, however, 

 as it enters the tibia it swells to a diameter of about - 5 -^ of an inch, then contracts again 

 to -g^o, and then again, at the apical extremity of the tibia, once more expands to -^>q. 

 Moreover, as in Gryllus, so also in Formica, a small branch rises from the upper sac, 

 runs almost straight down to the tibia, and falls again into the main trachea just above 

 the lower sac. The remarkable sacs at the two extremities of the trachea in the tibia 

 may also be well seen in other transparent species, such, for instance, as Myrmica rugi- 

 nodis and JPheidole megacephala. 



At the place wdiere the upper tracheal sac contracts there is, moreover, a conical 

 striated organ (x), which is situated at the back of the leg, just at the apical end of the 

 upper tracheal sac. The broad base lies against the external wall of the leg, and the 

 fibres converge inwards. In some cases I thought I could perceive indications of bright 

 rods, but I was never able to make them out very clearly. This also reminds us of a 

 curious structure which is found in the tibia of Locustidaa, between the trachea, the 

 nerve, and the outer wall, and which is well shown in some of Dr. Graber's figures. 



L b' 



Other Organs of the Prothorax. 



The anterior pair of spiracles, as already mentioned, lie (PL XL figs. 4, 5, Sp l ) between 

 the pro- and mesothorax. The tracheal tube immediately behind the spiracle is provided 

 with a short muscle, as already described in other insects by MM. Landois and Thelen*. 

 The ganglion (PI. XL figs. 2, 6, & 7, G l ) is of considerable size, and is connected ante- 

 riorly with that of the head, and posteriorly with that of the mesothorax, by a double 

 commissure. In the latter case the commissures pass through an orifice in the antefurca, 

 which thus not only serves as a support to the muscles, but also as a protection to the 

 nervous system. 



The oesophagus passes straight through the prothorax, and, indeed, does not enlarge 

 into the crop until it reaches the enlarged part of the abdomen. In the upper part of the 

 prothorax lie the large thoracic salivary glands (PI. XL fig. 2, gl). 



A considerable part of the upper and anterior portion of the prothorax is occupied by 

 the thoracic salivary glands, which I have already described in the ' Microscopical Journal. 



* Zeitsehr. f. wiss. Zool. 1867, p. 1S7. 



