THE PINE DESTROYEll. 109 



There comes in at this point, however, a question of structure 

 and arrangement which makes this tiny beetle an object of 

 profound interest. While some systematists put it with beetles 

 having five joints in each tarsus, others arrange it with the Tetramera 

 or four-jointed group. How, it will be asked, can such a curious 

 circumstance be explained ? The tarsus must have either four or 

 five joints, and it ought to be easy at once to decide the position 

 of the insect in systematic entomology by counting the joints. 

 Whatever ought to be the case, in this instance it is not easy to 

 decide which arrangement is the more accurate, and herein lies 

 the interest; because we find in the peculiar structure of the 

 tarsus in Hylurgus the connecting link between the two great 

 groups — Pentamera and Tetramera — by which the truth that 

 nature makes no leaps is again confirmed. 



The explanation of this curious phenomenon may be best 

 understood by the study of the accompanying diagram. If we 

 take a side view of the leg of Hylurgus (Plate X.) it is quite 

 certain that we shall be able to detect no more than four joints to 

 each tarsus, and under these circumstances we should be perfectly 

 justified in placing it among the Tetramera. If, however, by 

 careful manipulation we can get a front view of the leg, we find 

 that the third joint is of a somewhat peculiar shape, and has 

 developed into an abnormally large one, at the expense of the 

 fourth, which, while it may be said to exist, is in so rudimentary 

 a state as almost to escape detection. If its presence be admitted, 

 however, no matter how dwarfed and rudimentary its size and 

 form, it justifies us in placing it among the Pentamerous group. I 

 shall not be accused of straining a point if I remark that such 

 cases as these seem to suggest a process of development or 

 evolution, and thus tend to throw light upon one of the most 

 perplexing problems of the day. I must not here be tempted to 

 allude to analogous instances in other realms of nature, but pass 

 on to observe that there are several species of Hylurgus, of which 

 the best-known are — 



Hylurgus pilosus, Hylurgus crematus, and 



Hylurgus fraxini, Hylurgus pilaceus (?), 



about each of which Dr. Chapman wrote some very valuable 

 papers in the "Entomologist's Monthly Magazine'' of 1868 — 1869. 



