

OF THE LOWER VERTEBRATES < MI. 



These cones form simply the terminal members of a series which 

 extends inwards in the form of a curved column nearly to tin- inner 

 surface of the epidermis. Only the terminal members are strongly 

 cornified, the other members showing less and less cornification until 

 at a little distance down the series the cone is seen to be composed 

 of unmodified protoplasm containing at one side, near its base, a 



A. 



Fi'.. lf>. -Illustrating the devclopiiient of tin- larval t.-eth of Tadpoles. 

 A. J'.. ' ...nntliil'i : l>, /,'<(/</ f. //.,(,/.. (1) .-iftn (iut/cjt 



nucl.Mis. The run,, is in lad simply a cornified cell. Traced towards 

 tb- base of the column the cells are seen to bo composed of more 



irranular pi'dtoplasm and In h;i\c not yet developed a, lmlln\\. while 

 ibe cxtirm,' has.- of the column is funned by an initial cell of coiu- 

 parativ.-ly .-mall size and flattened shape. 



'I'ln! \\lml(; column is seen, then, to be composed of a seqnene.- of 

 conical tc'-th Inniiiii'j a replacement series, each tooth hein^ a single 

 cornilied cell. 



