436 PROCEEDINGS OF THE AMERICAN ACADEMY. 



terior margin, probably due to the greater development of the great 

 jaw muscles, as in this respect the large worker seems to resemble the 

 condition of the soldier in those species where there is a real soldier. 

 Moreover, there is another difference in the general shape of the head, in 

 that its greatest diameter dorso-ventrally is less in proportion to the 

 length of the head in the larger workers ; in other words, the heads of 

 the larger workers are somewhat shallower. 



3. In regard to the differences of some of the organs of the head, it 

 may be seen at a glance that the length of the antennae relative to the 

 size of the head is much less in the larger ants, they being hardly any 

 longer by actual measurement than in the smaller ants. The number of 

 joints in the antennae seems to be here, as in Camponotus americaniis, 

 always the same, unlike Dorylus (Emery, :01^). There are, however, 

 some differences in the antennal parts. For example, in the smaller ants 

 the scape is slightly longer than the width of the head, while in the 

 larger individuals it is somewhat shorter. In heads of intermediate 

 size the condition is variable ; sometimes the head is wider than the 

 length of the scape, sometimes the reverse is true, regardless of the 

 size of the head. In the larger ants the funiculus is only slightly 

 longer than in the smaller ones, and in proportion to the size of the 

 head it is much shorter. In proportion to the length of the scape it is 

 shorter in the larger ants. The scape itself is also of a different shape 

 in the two extremes ; in the large ants it is larger at the distal end 

 than at the proximal end, whereas in the small workers it is nearly 

 uniform in thickness throughout its length. 



4. Again, it was found that in the larger ants the compound eyes 

 are set slightly further back, as may be seen especially in side view, 

 and that they are also somewhat further from the margin of the head. 



5. The clypeus presents a good deal of difference in the two extremes ; 

 in the larger ants it is much thinner dorso-ventrally and only slightly 

 arched on the dorsal surface, while in the smaller ants the arch becomes 

 higher and more angular. Moreover, there is a considerable difference, 

 as seen from the dorsal side, in the shape of its outline, which is nearly 

 rectangular in the large individuals, and somewhat hexagonal in the 

 small. 



6. In the larger workers the frontal carinae (Wheeler, :10, p. 18) are 

 slightly farther apart in proportion to the total length of the head. 



7. The mandibles are not very unlike in the two extreme sizes, but 

 are, on the whole, more strongly built in the large workers. All the 

 teeth are fairly large in the large workers, but in the small workers the 

 outside ones are the stronger, though the difference in strength is not 

 great. 



