17 



Irregular Elongate Tunnels. — The egg-tunnels of Dendroctonus, Hylastes, and 

 Hylurgops are elongate, longitudinal, variably irregular, branched or winding, 

 and frequently anastomosed. 



Irregular Short Tunnels. — Several species of Dryocoetes, and others, cut short 

 irregular tunnels. 



Simple Longitudinal Tunnels. — These are simple tunnels lengthwise of the 

 grain, moderately short and straight. They may or may not have a nuptial- 

 chamber or turning-niche at the base of the entrance-tunnel, but they have no 

 ventilation tunnels or turning-niches along the sides. Phloeosinus dentatus Say 

 cuts a rather elongate egg-tunnel with a distinct nuptial-chamber. Eccoptogaster 

 rugulosus Ratz., and E. Jf.-spinosus Say, cut shorter, simple tunnels without a 

 distinct nuptial chamber. Eccoptogaster picew Sw., cuts an entirely different 

 one; here the entrance-tunnel opens into a large nuptial-chamber, which gives 

 off, above and below, but not opposite to each other, a longer or shorter egg- 

 tunnel. E. unispinosus Lee, of the Pacific Coast, has tunnels very similar to 

 those of picece; these are properly of the forked type. Chramesus icorice Lee. 

 cuts short longitudinal egg-tunnels with a distinct turning-niche at the base of 

 the entrance-hole. Individual tunnels are frequently more or less oblique. 



Simple Trafisverse Tunnels. — These are cut by very few of our species, 

 except as individual variations from a different type. 



Forked Tunnels. — In this type, as here defined, the entrance-tunnel opens 

 into two egg-tunnels, usually somewhat curved, and diverging at a very wide 

 angle, or nearly in line. Apparently this type has been developed by the exten- 

 sion of a turning-niche, such as is now cut by C. icorice Lee, into a second egg- 

 tunnel. The tunnels of Phthorophloeus picece Sw. (PI. 4, fig. 7), illustrate well 

 the transition from the simple egg-tunnel with a turning-niche into a regular 

 forked type. In this species an egg-tunnel is cut from the base of the entrance- 

 tunnel, usually nearly transverse, though frequently oblique, and a second much 

 shorter egg-tunnel is cut from the base of the entrance-tunnel at a varying, 

 though usually wide angle with the first; or in other words, the turning-niche 

 has been extended somewhat and a few egg-niches cut on either side. The 

 tunnels of Phthorophloeus liminaris Harris (PI. 5, fig. 7) are usually well-developed, 

 with two egg-tunnels, one often somewhat longer than the other, nearly in line, 

 and shghtly incurved to meet at the base of the entrance-tunnel. The latter is 

 oblique and its base slightly engraves the wood at its junction with the two 

 egg-tunnels. In the process of their development the tunnels of liminaris have 

 probably passed through the stage in which we find those of picece to-day. 

 Leperisinus aculeatus Say cuts somewhat similar egg-tunnels in ash, but the 

 two branches are rather more distinctly arched from their junction with the 

 entrance-tunnel. The tunnels of Hylurgopinus rufipes Eichh., in elm, are of the 

 same type (PI. 5, fig. 6). The species cutting the tunnels thus far described 

 are usually monogamous. 



The tunnels of Pseudopityophthorus minutissimus Zimm. are peculiar, 

 straight and transverse, but crossed near the middle of their length by a short 

 vertical tunnel. They may be included under the simple transverse tunnels 

 (PI. 4, fig. 2). 



Radiate, or Star-shaped Tunnels. — These are cut by the genera Ips, Pityoph- 

 thorus (in part), Pityogenes, Pityokteines, Polygraphus, and others. The entrance- 

 tunnel opens below into a flat nuptial-chamber lying between the bark and the 

 wood, or often chiefly in the former. From the sides of this cavity the egg- 

 tunnels radiate in varying number, according to species and individuals, from 

 three or four to eight or nine. The species cutting these tunnels are polygamous 

 and each egg-tunnel is cut, usually, by a separate female, while a single male 

 cuts and occupies the nuptial-chamber. The tunnels of Orthotomicus ccelatus 

 Eichh. are roughly star-shaped, with the nuptial-chamber entirely in the bark 



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