OF THE DOR-BEETLE. 93 



must be noticed, that the joints of the legs are on the hinge-Uke 

 principle, so that they can move in one plane only ; and here it 

 may be pointed out that in man the action of revolving the hand, 

 or, as it is called, pronation and supination, is effected by the ulna 

 and the radius moving round each other in the forearm, but no 

 such arrangement is possible in the case of beetles, and would be 

 a very weak one if it were ; nevertheless, a motion of this kind is 

 necessary, and it is effected in a very perfect manner by the femur 

 being attached to a moveable portion called the coxa, which lies 

 in a hollow in the sternum, and is held there by very strong 

 ligaments ; it rolls round in a plane at right angles to that of the 

 joints of the legs, so that it is, in effect, like a ball-and-socket joint, 

 and at the same time is possessed of great strength. As the 

 femora are driven forcibly against the coxae when the beetle is exer- 

 ting its strength in digging, and as sharp particles of sand and dirt 

 would get between the parts, thus causing great friction, the under 

 sides of the femora have a space covered with hairs, which act as 

 cushions, and also as brushes, for sweeping the gritty particles 

 away. There is also an additional portion which appears to be a 

 protection to the joint between the femur and coxa, somewhat on 

 the same principle as that of the patella or knee-cap in man. 

 These portions are the trochanters, as may be seen more developed 

 in the intermediate and posterior legs than in the anterior pair. 

 It has been previously pointed out the posterior trochanters are 

 elongated and hooked at their tips for a sexual purpose. The 

 tibise of the posterior legs are more square in form than those of 

 the anterior, and on the outside have three prominent ridges. 

 These are useful to the beetle to push the earth behind it when it 

 is digging, also to give it a hold so as to be able to force itself 

 forward. The intermediate legs are very similar to the posterior, 

 but less developed. In some of the other species of this genus, 

 as G. sylvatiais (Panzer), and G. vernalis (Linnaeus), the posterior 

 tibiae have only two tranverse ridges. 



The mesothorax carries on its under side, properly called the 

 mesosternum, the intermediate legs, and on its upper side, or the 

 mesonotum, the elytra or wing cases, and when the wings are not 

 extended for flight, the mesonotum is concealed by the elytra with 

 the exception of the scutellum, or little shield, which appears as a 



