102 Zoologica: N. Y. Zoological Society [HI; 3 



1920) I have published an account of the stridulatory organs of 

 the larval and adult Passalus and have given reasons for believing 

 that all the members of colony are kept together by the shrill 

 sounds they are able to emit. 



During the summer of 1920 while in Trinidad and British 

 Guiana my son Ralph and I made a few observations on several 

 of the species of Passalus which are very common in rotten logs 

 throughout the jungle. Just under the bark the beetles make 

 large, flat cavities, which are later very often occupied by the 

 fungus-growing ants of the genera Apterostigma, Myrniicocrypta 

 and Cyphomynnex, and evidently furnish just the right places 

 for their more or less globular gardens. In each of the Passalus 

 colonies examined during July and August there were only two 

 adult beetles, usually accompanied by a troop of larvae varying 

 little in size and evidently belonging to a single brood. In one 

 log, however, we found a pair of the beetles guarding a batch of 

 about 40 large, olive-green, broadly elliptical eggs, some of which 

 had just hatched. The young larvae closely resembled the older 

 individuals in the structure of the peculiarly modified paw-like 

 metathoracic legs, which are rubbed over the finely ridged middle 

 coxse during stridulation, but the hairs on the body were conspic- 

 uously longer and coarser. Our observations on the beetles and 

 their larvae both in the field and in the laboratory, confirm the 

 statements of Ohaus. 



The preceding account of the Platypodids, Scolytids and 

 Passalids will suffice to show that they have reached a more 

 advanced stage of social development than Coccidotrophus and 

 Eunausibius, though the latter exhibit certain interesting resem- 

 blances to such ambrosia beetles as Xyloterus. The two Silvanids 

 really represent a stage in social development intermediate 

 between that of the families mentioned and the merely gregarious 

 Silvanus, Oryziephilus, Nausibius etc. Although the colonies of 

 Coccidotrophus and Eunausibius are founded by pairs of parent 

 beetles and in the climax stage of their development may comprise 

 a considerable number of offspring in all stages of development, yet 

 the latter do not seem to be the recipients of any special care on 

 the part of the parents, unless we interpret as such the guarding 

 of the petiolar cavity and the deepening of the food-grooves which 

 would seem to render the nutritive parenchyma more accessible 



