TADPOLES. 101 



By drawing an imaginary line across between the 

 mandibles the lip may be divided into an upper and a 

 lower portion, the series of teeth above the upper 

 mandible being termed upper labial, those below the 

 lower mandible bein^ lower labial. These are described 

 as first, second, third, &c, proceeding from the outer 

 border towards the beak in both the upper and lower 

 sections of the lip, as shown in the accompanying 

 figures (p. 99). Each series is reckoned as one, 

 whether continuous or more or less interrupted in the 

 middle ; this method being far more simple, and at the 

 same time more correct, considering the great amount 

 of individual variation, than those used by some authors 

 who distinguish between "median" and "lateral" 

 series, according as to whether or not the series is 

 broken up in the middle. The first series, either in 

 the upper or lower division of the lip, may be marginal 

 (Fig. 42, a, t.l), or it may be within the border, 

 which is then occupied by fleshy papillae (Fig. 42, 

 b). The arrangement of the series is expressed 

 by a formula — § , for instance, indicating the number 

 in the upper and lower divisions, the figures being 

 separated by a transverse line corresponding to the 

 position of the horny beak. The labial teeth are 

 usually arranged in a single row on each ridge (Fig. 

 42, a) ; in the Disco glossidas, however, each ridge, or at 

 any rate the second, bears two or even three rows of 

 teeth (Fig. 42, b). The beak itself is made up of 

 horny elements like the labial teeth ; its edge, when 

 sufficiently magnified, is seen to be denticulate, each 

 denticle representing the cusp of a single tooth. 



The inside of the mouth and the pharynx (Fig. 44) 

 are beset with long pointed mucous papillae, " taste- 

 organs " of F. E. Schulze, the longest of which border 

 the choanae (ch), one in front and one behind, and are 

 followed by a pair with a denticulate fold between 

 them ; a cushion-like, hemispherical swelling (t) repre- 

 sents the tongue, on the anterior border of which a 

 pair of papillae are inserted. A broad cleft with 



