DE. 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 

 raentum (comp. 0. duivenhodli, PI. XC. fig. 5 a). 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 

 base 1. The length of the antennae 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 Prothorax, &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 (PI. 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 \a still 

 more remarkable in 0. burmeisteri (PI. XCII. figs. 5, G) than in 0. alces. 



The front tibiae, 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- 

 stemal processes are also proportionately more strongly developed in the males. 



(5) Evidence in favour of the Gradual Differentiation of the Male Forms hj 

 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 2) 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 0. alces, 0. bellicosiis, and 0. siva, in the first of which the telodont 

 form (PI. LXXXVIII. fig. 1) is one stage lower than in 0. alces, while 0. siva stands 

 another step lower, never passing, even in the highest forms, beyond, the amphiodont 

 stage (PI. LXXXVI. figs. 1, 2). But in the case of these species it is always possible that 



' In 0. hrool-eunus the broad quadrangular labrum of the telodont form (PI. XCV. fig. 13) is reduced to 

 a minimum in the priodont form (fig. 15). 



^ These could only be obser^-ed in the smallest males of Lucanus cervus. 



3o2 



