1921] Wheeler: Some Social Beetles 115 



ing from the young Tachigalia as a whole or perhaps even from 

 the nutritive parenchyma in its petioles, but the attraction of 

 these odors is probably due to their having acquired a "meaning" 

 for the beetles, because the latter throughout their larval and 

 early imaginal stages fed on these very substances, and had, in 

 fact, long been familiar vi^ith the petiolar cavities, the coccids, etc. 

 The latter part of this statement also applies to the young queens 

 of the obligate Tachigalia ants of the genera Pseudomijrma and 

 Azteca and would account for the rather unusual attachment of 

 these insects to a definite host-tree. Hence in these cases organic 

 memory, or "mneme," or even individual memory yields a more 

 satisfactory explanation of the phenomena than a naked tropism. 



A consideration of the responses to light leads to similar 

 results. The beetle colonies, as we have seen are "photophobic," 

 or live in the dark, and when the petioles are opened in the light 

 the insects are at first much agitated but soon settle down and 

 continue the regular routine of their existence even when the 

 pieces of petiole are kept exposed to artificial or diffuse day-light 

 in the laboratory. The adult beetles have well-developed eyes 

 and the larvae have three pairs of small simple eyes on each side 

 of the head. (Plate VII, fig. 2, Plate VIII, fig. 10). And since a 

 certain amount of light enters the petiole through the entrance, at 

 least when it happens to be unguarded, it is probable that under 

 ordinary conditions the eyes are mainly useful in enabling the in- 

 sects and particularly the larvse, to stay in the dark. There is noth- 

 ing to show that the young beetles, which leave the petioles to 

 establish new colonies, do so because they become positively 

 phototropic. The emigration may, perhaps, take place at night 

 and even if it occurs during the day the light in the parts of 

 the jungle where the young Tachigalias are growing, is very 

 subdued. I believe that the young beetles must emigrate either 

 because the space in the petiole has become too greatly reduced 

 by the growth of the colony or because the food-supply has for 

 the same reason become insufficient. In either case emigration 

 would be due to internal stimuli ("physiological states") . These 

 may also be important factors in the swarming of ants, bees and 

 termites. We might, perhaps, even suppose that the guarding 

 of the entrance by the beetles is due to an abortive or inhibited 

 emigration impulse due to feebler or vaguer internal stimuli 



