ACULEATA. 

 FORMICID.^. 



The ants (PL XL, Figs. 186-189, p. 238, Formica 

 Pennsylvanica, De Geer) have the rings of the thorax 

 much more loosely connected than in the typical 

 Hymenoptera. There is also less concentration of 

 these parts in the wingless workers (PI. XL, Fig. 188, 

 b\ b'\ ^"') and soldiers (PI. XL, Fig. 189, b\ b'\ 

 ^'") than in the winged males (Fig. 186, b\ b'\ ^'") 

 and females (PL XL, Fig. 187, b\ b'\ <^"'). This 

 is only another illustration of what we have already 

 pointed out, viz. that the consolidation of the thorax 

 depends upon the insect's power of flight, and is great- 

 est in the best fliers, and least in the poorest. The ab- 

 domen is pedunculated in all the forms ; but in the 

 stingless ants the peduncle has only one joint, while in 

 many of the stinging species it has two. This last 

 fact favors the view advanced above, that the peduncu- 

 lated abdomen is probably a result of the habit of 

 using the ovipositor as an offensive weapon. 



The male and female have both compound eyes 

 and ocefli (see Figs. 186, 187), but the worker and 

 soldier have no ocelH (see PL XL, Figs. 188, 189). 

 The mandibles of the soldier are organs of defence, 

 and are, therefore, larger and stronger than in the 

 other forms. The legs are strong : PL XL, Fig. 190, is 

 238 



