402 DE. F. LEUTHNEK ON THE ODONTOLABINI. 



(c) Modifications of various Parts of the Body. 



The varying size and shape of the mandibles affect the other parts of the body by 



the law of correlation of growth. They react first upon the size and shape of the head 



(the mouth-parts, the frontal crest, the spine behind the eyes, and lastly, the length of the 



antennae), and, secondly, upon the size and shape of the prothorax, especially on its width. 



1. Modifications of the Head. 

 If a species was a fixed and unchangeable entity, the small specimens would 

 reproduce the characters of the large ones, but on a smaller scale. The multiform 

 mandibles completely dominate the head. It is a generally received axiom in the 

 anatomy of Vertebrates that the thicker the muscles which are attached to the bones, 

 the more numerous ridges and protuberances do the latter exhibit. What a striking 

 difference exists between the skulls of old and young vertebrate animals — for instance, 

 between the skulls of a young and of an old Gorilla, where the muscles of the jaw are 

 so strongly developed in old specimens that the whole appearance of the head is quite 

 altered! The same law applies to the heads of our beetles, in which the chitinous 

 covering of the exocranium is likewise altered and enlarged by the development of the 

 muscles of the jaws. But in this case the impression on the external skeleton, which 

 is unalterable in the imago (which does not moult), is fixed upon it previously in the 

 plastic pupa-stage. (But the imago is little more than the elegant wedding-garment, 

 as Karl Ernest von Baer has so admirably called it.) It therefore follows that the 

 larger the mandibles, the larger must be the masseter muscles contained in the head, 

 and especially the hinder part of the head itself 



1. In the telodont form the head is broad in front between the eyes, the clypeus is 

 much elevated, and (for aerostatic reasons ]) the frontal crest is always strongly expanded 

 in front (PI. LXXXIX. fig. 2). 



2. In the mesodont form (fig. 3) the frontal crest is wanting, the front margin is 

 strongly indented, and the head is narrower between the eyes, but much broader 

 behind, where the principal muscles which move the mandibles are attached ; and the 

 line of attachment of the muscles which is thus formed may have given, through outward 

 expansion, rise to the spine behind the eyes (the principal morphological character of the 

 genus Odontolabis), which slopes obliquely backwards. 



3. In the small amphiodont and in the smallest priodont forms, the skull becomes 

 very flat, and the hinder part grows narrower and narrower (fig. 7), so that the head 

 finally appears broadest in front between the eyes. The spine behind the eyes also 

 becomes smaller and more pointed, and disappears entirely in some species, although 

 not in 0. aloes (comp. 0. lacordairii, VI. XCIV. fig. 5) ; it is entirely absent in the 

 female (fig. 8), in which the hinder part of the head is concealed by the prothorax, so 

 that the eyes almost touch the front edge of the latter. 



The mouth parts are considerably affected, for purely mechanical reasons. In the 



