OF THE TADPOLE. 113 



magnifying power to see them. 'Fhis ridge, with its crenated edge 

 furnished with these little bristles, extends entirely around the 

 mouth, the sides, however, being quite free from bristles, but 

 instead it is there worked up into a series of small, digit-like 

 processes, apparently extremely soft and delicate. 



The fleshy fringe thus surrounding the mouth proper is much 

 longer on the under than on the upper side, and apparently 

 capable of a certain amount of extension, so as with the upper 

 portion to form very effective lips, inside which are the true teeth. 

 These are formed from the epidermis, which rapidly hardens, and 

 as the intestine is forming farther back in the body, these are 

 developing on what was a short time previously the inner portion 

 of the lips. 



The teeth in the upper jaw are arranged in a series of points 

 behind each other, and in the lower, they take the form of a number 

 of parallel serrations. A diagram of the upper rows is given in Plate 

 XII., Fig. 7, and an enlarged diagram of the mouth in Fig. 6 of the 

 same plate. Immediately behind the lower teeth inside the 

 mouth there is at this period a decided protuberance, or pad, 

 furnished at its very tip with a small projecting point, and on the 

 upper portion of the palate an invagination of the epidermis 

 occurs, filled with granular matter. This invagination is the 

 internal opening of the nasal organ, which stretches from the 

 mouth upwards into close proximity with the fore-brain, and then 

 bending round at approximately a right angle opens again on the 

 outside above the mouth, forming the external nostrils. The 

 granular matter with which the cavity is filled has, for the most 

 part, no definite shape ; but near the internal opening it presents, 

 in some cases, the appearance of round, nucleated cells, with two 

 delicate extensions proceeding from each of them. The wall of 

 the cavity consists of square nucleated cells, packed closely 

 together, arranged generally in a single row, but for a portion of 

 the boundary it appears as a double row. At the internal opening 

 of the cavity is a small protuberance, formed by a projection of 

 the lower edge of the epithelial layer, and the whole orifice is 

 nearly closed by a pear-shaped organ, abruptly pointed on the 

 anterior, and connected behind only with the true roof of the 

 mouth-cavity. 



