402 DR. F. LEUTHNER 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 
antennz), 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 (Pl. LX X XIX. 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 O. alces (comp. O. lacordairii, Pl. 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 
