The Genus Hylastes, Er. 133 
bark on which Hy/lastes feeds. The junction of the gizzard and the ventriculus 
is very distinct, being marked by a sudden constriction of the canal. This 
is rendered more distinct by the large size of the ventriculus, which is fully 
twice the diameter of the gizzard. The ventriculus tapers posteriorly to its 
junction with the stomach. The stomach is a long tube, narrow at its 
extremities but slightly dilated in its middle portion, which is further 
distinguished by the numerous villi or diverticula arising from it; these are 
short and usually curved. The stomach terminates at its junction with the 
intestine which, for convenience sake, may be said to be further distinguished 
by the opening of the malpighian tubules into it. The intestine is a long, 
narrow, coiled tube varying in diameter according as it is filled with frass 
is 
ps 
Fig. 14.—Gizzard of H. ater cut open to show structure 
(only half the organ is shown). 
or not. The malpighian tubules are six in number, and are arranged in two 
groups of two and four respectively. They are remarkably long, very narrow 
tubes, much coiled, and difficult to dissect out without mutilation. The 
foregut extends from the mouth to the prothorax; the midgut occupies the 
meso- and meta-thoracic regions; while the hindgut, together with the 
reproductive organs, fill the abdominal cavity. 
reproductive Organs of H. ater. (Plate IX. Figs. 15-18, and 19.) 
The importance of an examination of the reproductive organs of the 
bark beetles, and, particularly, of a knowledge of those of the female, in 
studying the biology of a species has been insisted on by Nusslin. The 
state of these organs in the female is a valuable key to her sex maturity 
and even to her approximate age. 
Male Reproductive Organs (Fig. 15),—These comprise the testes, the paired 
vasa defercntia with their sperm sacs and diverticula, the unpaired vas deferens, 
and the penis. The testes are two in number, lying on either side of the median 
Jine. Viewed ventrally, they appear as flat discs; laterally, they appear 
