DR. F, LEUTHNER ON THE ODONTOLABINI. 403 
largest telodont and mesodont forms (figs, 1, 3) the clypeus and the labium (with which 
it is united) are depressed below the mandibles (toothless at the base) as far as the 
mentum (comp. 0. duwivenbodii, Pl. XC. fig. 5a). In the amphiodont and priodont 
forms (figs. 5, 6) the clypeus is flat, and the labrum is contracted into a triangular 
epistoma above the closed mandibles, which are flattened and toothed at the 
base1, The length of the antenne of the male, dependent upon the stronger 
development of the scape, is always exactly proportioned to the length of the head. 
2. Modifications of the Prothoraz, &c. 
The changes of form in the prothorax, when carefully investigated, are found to be 
just as important as those of the head. While the prothorax is trispinose in large 
specimens, having two deep depressions on each side (Pl. LXXXIX. figs. 1, 3), the 
front angle disappears in the smallest priodont specimens, in which the form of the 
male resembles that of the female (figs. 7, 8). The narrowing of the prothorax is still 
more remarkable in 0. burmeisteri (Pl. XCII. figs. 5, 6) than in O. alces. 
The front tibiz, even in the smallest males, are always longer than in the females, 
owing to the longer head and mandibles. For the same reason, the pro- and meso- 
sternal processes are also proportionately more strongly developed in the males. 
(5) Evidence in favour of the Gradual Differentiation of the Male Forms by 
Modification of the Mandibles, 
We have already shown that in 0. alces an unbroken series of male forms exists, 
from the largest with most highly developed mandibles to the smallest, in which the 
mandibles resemble those of the female. The next problem which confronts the 
observer is whether the small priodont forms may not be specimens in which the 
mandibles are imperfectly developed. 
The idea that the so-called degenerated forms should be regarded as neuters, was 
refuted by an examination of the fully developed and even comparatively large sexual 
organs, in which not only the chitinous parts, but also the testes and their contents 
(the spermatozoa”) were found to be well developed in the smallest males. 
As the middle-sized forms generally possess much more strongly developed and com- 
plicated mandibles, it appears very probable that the telodont form was gradually 
developed from the priodont form. We may suppose this to have been the case with 
the progenitors of O. alces, O. bellicosus, and O. siva, in the first of which the telodont 
form (Pl. LXX XVIII. fig. 1) is one stage lower than in O. alces, while O. siva stands 
another step lower, never passing, even in the highest forms, beyond. the amphiodont 
stage (Pl. LXXXYVI. figs. 1,2). But in the case of these species it is always possible that 
1 In O. brookeanus the broad quadrangular labrum of the telodont form (Pl. XCY. fig. 13) is reduced to 
a@ minimum in the priodont form (fig. 15). 
? These could only be observed in the smallest males of Lucanus cervus. 
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