COLEOPTERA SCOLYTID^E. 89 



If we take, therefore, the middle of the mother-gallery as a centre, we 

 shall see that the larval galleries, in a geometrical structure, somewhat 

 resemble the stones forming an arch, inasmuch as they all radiate 

 from a common centre. In fig. 82, b, we have a very short mother- 

 gallery, with radiating larval galleries. In fig. 82, r, we have a single- 

 armed mother-gallery and right-angled larval galleries. 



In fig. 82, d, we have a double-armed horizontal mother-gallery, 

 with practically right-angled larval galleries. In fig. 82, e, we have 

 similar mother galleries of a polygamous species. In fig. 82,/, we have 

 a four-armed mother-gallery, with right-angled larval galleries. 



In fig. 82, g, we have practically a repetition of 82, b, except that 

 the mother-galleries are horizontal. 



In fig. 82, h, we have a star gallery formed in a slightly different 

 way, inasmuch as the circular central portion is made by the male, 

 and the female galleries radiate from the male chamber, while the 

 larval galleries again radiate from the mother-gallery. 



In the foregoing it should be noted that all the young beetles finally 

 leave (swarm) by gnawing new flight-holes ; but in the remaining 

 figures, as representing distinct wood-borers, the young beetles finally 

 leave (swarm) through the old bore-holes. 



In fig. 82, i, we have a " ladder gallery " in wood, where the mother- 

 gallery is horizontal and the larval galleries perpendicular. The larval 

 galleries are very short, as in Trypodendron lineatum. 



In fig. 82, li, we have forked mother and larval galleries, making 

 collectively a sort of gallery of pipes, as it were, on a comparatively 

 even plane, as in T. mohographus} 



In fig. 82, I, we have a representation of a horizontal mother-gallery 

 and perpendicular larval galleries. It may be considered as illustrative 

 of T. dispar. 



In fig. 82, m, we have a representation of a family-gallery, as in T. 

 Saxesenii. 



The generations of the Scolytidse are very variable. In the German 

 literature we note two or more broods per year of a species which only 

 produces one brood in the north of England ; and again we get some- 

 times two broods per annum of a species in the south of England 

 which only produces one brood a-year in the north. These varia- 

 tions are by no means universal, but the student must be careful to 

 note them. 



1 This species is not found in England. 



