HETEROGONY AND TAXONOMY 



209 



(1) Prionodont. Mandible beset with inwardly-directed teeth 

 throughout its length (2 sub-forms). 



(2) Amphiodont. A toothless gap on the mandible, separat- 

 ing ' prebasal ' and ' sub-apical ' teeth. 



(3) Telodont. Pre- 

 basal teeth lacking. 



(4) Mesodont. With 

 a new, single 'sub- 

 median ' tooth, on the 

 ventral side (2 sub- 

 forms) . 



(5) Mesamphiodont. 

 Numerous teeth in 

 homologous position 

 to sub-median tooth 

 of (4) ; and also a set 

 of teeth in position 

 of pre-basals of (2). 

 (Fig. 91.) 



These types grade 

 into each other imper- 

 ceptibly, and the dis- 

 tinctions are admit- 

 tedly arbitrary : e.g. 

 a specimen is classified 

 as Amphiodont if a 

 gap is present which 

 is considered larger 

 than the normal gap 

 between two teeth, 

 Prionodont if it is con- 

 sidered not to exceed 

 this size. Further- 

 more, there is a 

 correlation between 

 tooth-type, mandible- 

 size, and body-size, 

 the five types, in the 

 order listed above, succeeding each other with increase of size '> 

 and even within each ' form ' there is a trend, with increasing 

 size, away from the type of the previous form and towards 

 that of the one succeeding. 



It might be at once concluded, one would think, that all 

 14 



Fig. 91. — (1) Female and (2 — 6) five different- 

 sized males of the stag-beetle, Cyclommatus 

 tarandus, to scale, to show the change in form 

 and relative size of the male mandible with 

 increase of absolute body-size. 



Male forms : 2, prionodont ; 3, amphiodont ; 4, telodont ; 

 5, mesodont ; 6, mesamphiodont. 



