DR. F. LETJTHXER ON THE ODONTOLABI>;i. 



405 



tooth gi'adually disappears. Finally, nothing but the front tooth remains at the tip, 

 which becomes considerably curved inwards, like a hook (no. 1). 



Here too, as in 0. alces, we pass without a break (but from an amphiodont form which 

 most resembles the female) to the terminal form by gradual lengthening and simplifica- 

 tion of the mandibles. But no one will ever be able to prove the opposite, as the small 

 forms of mandible are always more complicated in structure. A more complicated form 

 can never arise from a more simple form by arrest of development. 



The results at which we arrived through the study of 0. alces are thus confirmed, 

 and we are consequently obliged to regard the mesodont, amphiodont, and priodont 

 forms as stages of the development of the mandibles, and as antiquated forms which 

 still reappear from causes which we do not understand. The smallest male is so similar 

 to the female that one of the most eminent entomologists, who first described 

 Eeterochthes hrachijpterus, an allied species, mistook one of these small males for a 

 female, and described and figured it as such ^. 



But if, instead of studying Coleoptera, in which the metamorphosis is complete, and 

 each imago can only represent a single form, so that its history can only be studied 



Pig. 5. 



Head and buccal apparatus of Anosfostoma mistmlasite. 

 No. 1, full-grown (J; no. 2, ditto, side view; no. 3, full-gro-n-n J ; no. 4, early larval stage of J 



■with mandibles like those of 5 . 



by a phylogenetic method and by series, we were dealing with insects with incomplete 

 metamorphoses, in which we might be able to trace the gradual development of the 



' Trans. Ent. Soc. Lond. (3) ii. pi. x. fig. 6. 



