90 THE EXTERNAL ANATOMY 



Having found some fresh dung of almost any animal — and it 

 evidently does this by the sense of smell, which faculty it must 

 possess in great perfection — the beetle sets to work and digs a 

 hole under it into the ground, perpendicularly, to the depth of 

 eight or nine inches, and at the bottom of it places a ball of the 

 same, as food for the future larva. There are several species of 

 Dor-Beetles, some of which are not so common as others, but the 

 one chosen is that which abounds, I believe, everywhere, and most 

 certainly in Somersetshire. It is Geotrupes spiniger (Marsham), 

 synonymous with G. ?nesoleius (Thoms). It probably received the 

 name spiniger — or prickly — from the fact of the male possessing a 

 large tooth bent downwards on the under sides of each of the 

 anterior tibiae (PI XL, Figs. 8 and 9) ; a large hooked tooth on 

 each of the posterior femora ; and a hooked process at the tip of 

 each of the posterior trochanters (Figs. 6 and 7). All these are 

 evidently sexual developments, giving the male a better power of 

 grasping. It varies very much in size, as in fact do all those 

 beetles which in the larval state feed on a supply of food placed 

 for them by the parent, or in any way have to get a precarious 

 living ; whereas plant-feeders and those that subsist on substances 

 of which there is an abundance, are very constant in size. Speci- 

 mens of the Dor-Beetle may be met with nearly one inch in 

 length, and small ones, scarcely more than half this length, may 

 occasionally be found. 



I now propose to notice the principal external parts of this 

 beetle, commencing with the head and mouth organs. The head 

 is very hard and strong, and the clypeus has a ridge down the 

 centre, so that both vertically and laterally it is of a wedge-like 

 form. The situation of the eyes is peculiar, for a very hard band 

 of chitine is continued from the sides of the clypeus, so as to 

 encircle and divide each eye in such a way that a portion of the eye 

 appears on the upper side of the head and a larger portion on the 

 lower side (PI. XL, Figs, i and 2, b and c). Without this protection 

 it is evident that as the beetle worked its way into the ground head 

 downwards, the eyes would be damaged. The short antennae 

 consist each of eleven joints, which in the Coleoptera is the 

 normal number. The first joint is by far the longest, and the last 

 three form a trilamellate club, as previously described. When the 



