FAMILY SCOLVTIDAE 465 



at rij^ht aiij^lcs to it : tliosc; in the lower part of the jj:allery— i.e. that p(jrtion 

 tirst made by the mother beetle — have a downward direction, whilst 

 those in the upper part trend in an upward direction. The larval fj^alleries 

 are approximately equal in length to one another, and when completed the 

 plan made by the mother and larval galleries has the shape of an elongate or 

 blunt ellipse, the long diameter being formed by the egg-gallery. When 

 full-fed the grubs either pupate in the enlarged end of their gcdlery or may 

 hollow out a shallow chamber in the sapwood or bark and pupate in this. 

 In both cases the beetles on maturing bore straight through the bark above 

 them and leave the tree. In any event, the " plan " left by the operations of 

 the mother beetle and larvae is always constant for that species, and enables 

 its former presence to be easily recognized. A comparison of the plans 

 of the gallenes oi Scolytus juajor (frontispiece) and Sphacrotrypes siicalikcnsis 

 (fig. ig on p. 33) will render this evident. 



In the polygamous forms (which are typically represented by the Indian 

 Polygraphns, Tovikus, and Pityogenes) the male beetle tunnels through the bark 

 till it reaches the bast or outer sapwood, and eats out in either or both a 

 small irregular-shaped depression, which forms the pairing-chamber, and 

 remains in this. A female enters the pairing-chamber either by enlarging 

 the entrance-tunnel of the male if she is of larger size than the male 

 (which is often the case), or by boring an entrance-tunnel of her own \vhich 

 accuratel}- hits off the pairing-chamber. On joining the male she is 

 fertilized," and then at once commences eating out an egg-gallery which 

 takes off from the pairing-chamber in an upward direction, but runs more or 

 less parallel to the long axis of the tree. A second female now enters the tree 

 by the entrance-tunnel of the male or that of the first female, and on 

 reaching the pairing-chamber pairs in her turn with the male and then eats 

 out her egg-gallery, which she carries in a direction opposite to that of the 

 first female. If a third female enters, her gallery is taken up the tree, whilst 

 that of a fourth will proceed ciownwards. In either event the galleries of 

 the second and fourth females will diverge outwards from those of the 

 first and second females, and will never cut into the latter. Each female as 

 she eats out her gallery bites small notches in the sides and lays an egg in 

 each. These notches are not, however, eaten out in the same regular 

 manner as is the case with the monogamous bark-borers, nor in some cases 

 are the eggs placed so close to one another. Also the major portion of the 

 eggs are laid on that side of the gallery which is farthest from that of the 

 ndghbouring female egg-gallery (cf. fig. 328). In some cases, as e.g. Tomicm 

 rihhcntvopi, the egg-galleries, with the notches in which the eggs are 

 deposited, groove the sapwood deeply, whilst the larval galleries are eaten 

 out in the bast only, and so are not visible on the sapwood (cf. pi. xl). 



The larval galleries, which are eaten out by the grubs on hatching in a 

 manner similar to that above described, are not so uniformly regular, and 

 ma>- wind about more. They are, however, always taken in a direction 

 away from the egg-gallery, instinct appearing to teach the grub that no 



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