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dens which emerged from a desk which had been in use for thirty 

 years. He suggests that such prolonged Hves are a kind of starvation 

 sleep analogous to winter sleep. McNeil ('86) records that the beetle 

 Ehuria quadrigeniinata (PI. XXVIII, fig. 5) emerged from a door- 

 step in a house which had been built nineteen or twenty years, and 

 Packard ('90, pp. 687-688) records the emergence of the wood- 

 boring beetle Monohammus confitsor Kby., which came out of a piece 

 of pine furniture which had been in use "for fully fifteen years." 

 Felt ('05, p. 267) states that instances are recorded of Chion ductus 

 (PI. XXVIII, fig. 2) emerging from wood several years after the 

 furniture had been manufactured. The prolongation of the life cycle 

 of Elaphidion villosmn (PI. XXIII, figs. 3 and 4) in dry wood is 

 another case bearing upon this point. Other similar cases are known 

 which show that larval life is greatly prolonged in dry wood, or that 

 the adult in such conditions lives for many years. In such cases it is 

 not known just when the adult transformed. 



Animals which live in living bark and living wood are in some 

 cases, with regard to moisture and to air, subject to peculiar conditions 

 brought about by the sap of the tree. In-the case of hardwoods the 

 sap is watery, and in conifers the pitch or turpentine is gummy and 

 easily mires feeble insects, or suffocates them. Why is it that in hard- 

 woods, such as maple and box elder, all wood- and bark-boring in- 

 sects are not flooded in their burrows and drowned by the flow of sap 

 in the spring? I do not know how many factors are involved in this 

 problem. The gummy exudation on peach and cherry trees is evi- 

 dence of the influence of insects upon the flow of sap. Where sap 

 flows from trees many insects, particularly flies and Lcpidoptera, are 

 attracted to and feed upon this fluid. Felt and Joutel ('04, p. 17) 

 state that the grubs of some members of the beetle genus Saperda 

 feed upon the sap, but they do not give the evidence for their opinion. 



In the coniferous trees the flow of pitch has a marked influence 

 upon the bark-inhabiting scolytids. Hopkins ('99, pp. 404) says of 

 the pair of Dendroctonus frontalis, which work together to establish 

 the brood, that "In this operation in healthy living bark filled with 

 turpentine, it is necessary for one of the beetles to move back and 

 forth in the burrow continually in order to keep it open and push back 

 and dispose of the borings and inflowing turpentine. . . . From 

 the time they penetrate the outer layer of living bark there must nec- 

 essarily be an incessant struggle with the sticky, resinous mass which 

 is constantly flowing into the burrow and threatening to overcome 

 them." The larva of another bark-beetle, D. terebrans, is able to live 

 in this sap. Thus Hopkins (1. c, p. 418) says: "This social brood 

 chamber is often extended down towards or even into the bark of the 



