1907.] Wheeler, The Polymorphism of Ants. 47 



converted them into food for the larvae which had not yet pupated? Or 

 did they stick to their hosts and pupate within the cocoons? In order to 

 ascertain, if possible, the true state of affairs, I transferred the whole colony 

 to a fresh nest and examined the soil of the old nest with great care. There 

 were no traces of the missing commensals. The only remaining resource 

 was to open the cocoons. Several of the cocoons which had been taken 

 with the nest October 27 had hatched, but by November 10 there were still 

 thirteen cocoons in the nests, as several of the larvae had pupated in the 

 meantime. Five of these were opened, and in two, which contained semi- 

 pupae of Pachycondyla and were, therefore, of recent formation, commensals 

 were found ! Having shared the table of their host, they had come to share 

 its bed as well. The Metopina, too, had pupated after the manner of its 

 kind — forming a puparium; i. e., instead of spinning a cocoon like the 

 ant larva, the dead larval skin, somewhat shriveled and contracted, was 

 used as an envelope, and within this the pupa proper was formed. 



This puparium, represented in Plate V, Fig. 69 v, is from 2.25 to 2.5 mm. 

 long and clearly of the cyclorhaph type. It is elliptical, much flattened 

 dorso-ventrally, especially along the edges, which are thin and hyaline and 

 almost alate. The brownish dorsal surface is thrown into delicate and 

 irregular transverse wrinkles. Anteriorly, in the thoracic region, there is a 

 pair of short black respiratory tubes. The ventral surface is very glabrous 

 and distinctly paler than the dorsal surface. 



Subsequently, several other cocoons were opened and two more were 

 foynd to contain the puparia of commensals. In all four cases the puparium 

 was invariably located in the caudal pole of the cocoon, just to one side of 

 the black blotch of ejecta deposited by the ant-larva before becoming a 

 semipupa. At this point the puparium was immovably stuck to the wall of 

 the cocoon by means of its smooth ventral surface. Its anterior end was 

 directed towards the cephalic pole. As there is always considerable space, 

 especially at the posterior pole, between the walls of the cocoon and the 

 enclosed ant-pupa, the much flattened fly puparium did not in the least 

 crowd its host. 



It would be interesting to know what the commensal larva is doing 

 while the ant-larva is weaving its cocoon. Does it move about to avoid the 

 swaying jaws of the spinning larva? Or does it take up its position from 

 the first at the posterior end of the larval ant and there remain motionless 

 while the posterior pole of the cocoon is being completed ? It is very diffi- 

 cult to answer these questions. The fact that the posterior poles of all the 

 cocoons containing puparia were somewhat distorted, being broader, more 

 obtuse, and more irregular than the normal cocoons, would seem to indicate 

 that the ant-larva may modify this end of its cocoon for the better accom- 



