14 



EGG-NICHES. 



The great majority of North American bark-beetles deposit their eggs 

 singl}^ in small niches, termed egg-niches, cut along the sides of the egg-tunnels. 

 These are shown distinctly in the illustrations of the tunnels of Leperisinus 

 aculeatus Say, Pityogenes hopkinsi Sw., Pityopthorus cariniceps Lee, and many 

 others given in this paper. Usually the niche is cup-shaped, with a circular 

 opening, and is somewhat deeper than the thickness of the eggs. The niche is 

 cut with the mandibles, and usually at the extreme end of the egg-tunnel as 

 thus far cut. The size of the niche in relation to the size of the egg varies with 

 the species. The tunnel face of the wall of egg-packing is usually slightly 

 convex, so that the cylindrical character of the tunnel is but little altered; 

 but certain species cut relatively small niches, with the result that the eggs 

 and their covering of dust project decidedly into the tunnel. 



EGG-POCKETS. 



These are large niches cut along the sides of the egg-tunnels by species of 

 Dendroctonus, Ips concinnus Mannh., Orthotomicus caelatus Eichh., and others, 

 in which several eggs are deposited and packed with boring-dust. 0. caelatus 

 deposits from two to eight eggs in a mass at the bottom of each pocket. 

 Dendroctonus simplex Lee, places three or four eggs side by side in the bottom 

 of an elongate shallow pocket or very short groove. The details vary consider- 

 ably with the species and with the environment, and apparently to some extent 

 with the individual. D. simplex often deposits a few eggs in the boring-dust 

 which fills portions of the tunnels. 



EGG-GROOVES. 



Dendroctonus valens Lee, Hylurgops pinifex Fitch, Dryocmtes americanus 

 Hopk., and others, deposit their eggs in layers or rows along one or both sides 

 of the egg-tunnels. The tunnel is widened or grooved for the reception of the 

 layer or layers of eggs and their invariable protective covering of boring-dust. 

 Hylurgops pinifex Fitch, often deposits three layers of eggs in one groove. The 

 continuous wall of egg-packing covering the egg layers is in line with the tunnel 

 wall so that the cavity of the tunnel is cylindrical, and but little larger than the 

 circumference of the beetles. Here again, the details vary greatly with the 

 species and often markedly in the same genus. Dryocoetes americanus Hopk.; 

 frequently deposits a few eggs in the roof of the tunnel. 



TURNING-NICHES. 



These are cut by Dendroctonus simplex Lee, and others, at intervals along 

 the sides of the egg-tunnels; they are rather wide and deep excavations, and 

 are used by the beetles for reversing their position, exactly as a street car or 

 railway train uses a " Y " in the track. I have only rarely found a few eggs 

 deposited in them. Certain species cut a short tunnel or a niche at the base 

 of the entrance-tunnel at an angle with the egg-tunnel; these serve in the same 

 manner for turning. The constructors of forked tunnels use the two branches 

 of the egg-tunnel and the entrance-tunnel for the same purpose. The ventilation- 

 tunnels, previously referred to, and the nuptial chamber are also used for this 

 purpose as well as for copulation. 



THE NUPTIAL CHAMBER. 



Many polygamous and a smaller number of monogamous species have a 

 distinct chamber in the inner bark at the base of the entrance hole, called the 



