15 



nuptial chamber, from which the egg-tunnels originate. The star-shaped tunnels 

 of Ips, Pityogenes, Pityophthorus in part, Polygraphus, and others, have a 

 distinctly flattened nuptial chamber, usually relatively large, either entirely 

 in the inner bark or engraving the wood surface. In the normal star-shaped 

 type the egg-tunnels radiate from all sides of the chamber; in the modified type 

 cut by Ips calligraphus Germ., Ips perturhatus Eichh., and others, the two or 

 three tunnels arise from the chamber at the opposite upper and lower sides. 

 The unispinosus group of Eccoptogaster cut a vertical tunnel above and below 

 from opposite sides of a rather large nuptial chamber (PI. 20, fig. 3). Two 

 other types of tunnels are cut by the species of the genus Eccoptogaster, as at 

 present constituted, one simple and vertical E rugulosus, the other forked 

 and transverse (PI. 4, fig. 1). The species of Phloeosmus cut a single vertical 

 egg-tunnel, usually with a large nuptial chamber at the base of the entrance 

 tunnel (PI. 5, fig. 5). Many modifications of the chamber appear in the 

 family, varying from the indefinite cave-tunnel with one or two irregular egg- 

 tunnels, cut by some Pityophthorus, to the perfectly star-shaped tunnels of 

 Pityogenes and some species of Pityophthorus and Ips. 



The beetles utilize the chamber for several purposes. It serves as a 

 temporary storage room for boring dust thrust into it by the females working 

 in the egg-tunnels; it is also used by the beetles for turning or reversing their 

 position, particularly by species which cut no ventilation tunnels; and it is 

 used regularly for copulation. With polygamous species the male spends nearly 

 all his time in the nuptial chamber and in the entrance tunnel. 



The nuptial chamber is a special modification, and has apparently arisen 

 independently in several groups of genera. The star-shaped tunnels of 

 Polygraphus, with a distinct chamber, are closely similar to those of some Ips 

 and Pityogenes; but the beetles are structurally so widely separated that no 

 community of origin could account for their similarity in habit. The chamber 

 is well developed in Eccoptogaster and Phloeosinus, and these genera are not 

 only widely separated morphologically from each other but also from the two 

 groups just mentioned. 



In the genus Pityophthorus we find evidence that the star-shaped type may 

 have arisen in this instance from the more primitive cave-like type still cut by 

 some species of the genus; and the habit may be explained in allied genera by 

 community of origin. In some species of Dr-yocoetes we find what appears to be 

 a secondary degeneration from the star-shaped type to irregular tunnels without 

 definite plan. The chamber has apparently arisen independently in Eccopto- 

 gaster, Phloeosinus, and others, as a simple enlargement of either the egg-tunnel 

 or the entrance-tunnel, at or near the junction of the two. 



FOOD-TUNNELS. 



The feeding habits of the adults vary greatly with the species. In the 

 process of cutting the egg-tunnels much of the excavated wood is swallowed, 

 and many species apparently obtain sufficient nourishment in this way. Other 

 species excavate special food-tunnels either before or after cutting the egg- 

 tunnels. The young adults may feed extensively before emerging from the bark, 

 cutting winding food-tunnels, " brood burrows," between the bark and the 

 wood, as with species of Ips, Pityogenes, and others; or they may leave the parent 

 tree directly from the pupal cell, and cut food tunnels in the bark of other trees, 

 as with species of Ips, Phloeosinus, Eccoptogaster, and others. The parent 

 adults may extend the egg-tunnels as winding food-tunnels, " terminal burrows," 

 or cut short food-tunnels elsewhere before beginning their second set of egg- 

 tunnels. This intermediate period of rest and feeding is needed, apparently, 

 in order to mature the second lot of eggs. * 



