1907.] Wheeler, The Polymorphism of Ants. 3 



it is often found in bottom lands and waste places where the soil is rich 

 and supports an open growth of grasses and especially of Crotons (Croton 

 texensls and C. monantJiogynus) . It is a harvesting species and stores the 

 flat chambers of its nests with innumerable seeds collected from all the 

 plants in the neighborhood. Like other harvesting ants, however, it does 

 not confine itself to a vegetable diet, but eagerly seizes on any insect food 

 that may fall in its way. 



In common with other members of the great genus Pheidole, instahilis 

 presents four phases known as the soldier, worker, female and male respec- 

 tively. The soldier is 4-4.5 mm. long. The shape and extraordinary 

 proportions of its head are shown in Plate I, Fig. 1, and Plate V, Fig. 63 o. 

 Its gaster is black and shining, the mandibles and clypeus are dark brown, 

 the remainder of the head, thorax and appendages reddish brown. 



The head is subopaque and elaborately sculptured as shown in the fig- 

 ure. The worker (PI. I, Fig. 7, and PI. V, Fig. 63 c) is only 1.5-1.8 mm. 

 long. It is shining throughout, and of a dark brown or black color with 

 yellowish appendages. The female (PI. I, Fig. 8 and PI. V, Fig. 63 a), 

 which measures 5.5-6 mm., is dull black, with the legs, antennte, mandibles 

 and anterior half of the head yellow. The wings (removed in the specimen 

 figured) are yellowish hyaline with pale veins. The male (PI. I, Fig. 9 and 

 PI. V, Fig. 63 e) is a much smaller and more graceful insect than the 

 female, measuring only 4-4.3 mm. Its head and gaster are black, its thorax 

 and appendages sordid yellow, the former with pale sutures. Its wings 

 resemble those of the female. 



While instahilis agrees with its congeners in having the four phases just 

 described, it differs from all except a small group of North American species 

 of Pheidole in presenting in every well-developed colony a series of individuals 

 intermediate in size, structure, and sculpture between the soldier (PI. I, 

 Fig. 1) and the worker (PI. I, Fig. 7). This series, which is very complete 

 in large colonies, is represented in Plate I by a few selected individuals 

 (PI. I, Figs. 2-5 and PI. V, 63 r). The occurrence of such intermediate 

 forms, though well-known in some other genera of ants, like Solenopsis and 

 Camponotus, is so unusual in the genus Pheidole as to call for the special 

 explanation which I shall attempt to give in the sequel. It is also an inter- 

 esting fact that the organs are not always reduced in size in strict correlative 

 proportions as we descend the series of intermediate individuals from the 

 soldier to the worker. As shown in Plate I, Figs. 5 and 6, for example, the 

 antennal scape may be of the same length in two individuals which differ 

 considerably in the size of the head. Or, again, as shown in figure 4, the 

 scape may be longer in one individual than in others with larger (PI. I, Fig. 

 3), or smaller heads (PI. I, Figs. 5 and 6). 



