TADPOLES 



57 



gill-chamber and the finny margins of the tail ; but the change 

 from the tadpole to the final Anurous animal implies an almost 

 entire reorganisation. 



In the earliest condition the embryo consists of a large head 

 and body, while the tail is still absent. Behind the beginnings 

 of the future mouth appears a transverse crescentic fold, with the 

 convexity looking backwards, which develops into the paired or 

 unpaired adhesive apparatus. This consists of large complex 

 glands, developed in the Malpighian layer, originally covered by 

 the cuticula, which soon disappears, whereupon the sticky secre- 

 tion enables the larva to attach itself to the gelatinous mantle of 

 the egg, later on to weeds or other objects in the water. The 

 name of suckers, often applied to this apparatus, conveys a wrong 



SpT. 



FIG. 9. Four stages of the development of the adhesive apparatus (A) of Bufo vulgaris ; 

 Af, Mouth ; Sp.T. spiracular tube. In 3 the gills are almost completely hidden by 

 the united right and left opercular folds. The small outlined figures indicate the 

 shape and natural size of the tadpoles. (After Thiele.) 



idea, there being neither muscles nor any suctorial function. The 

 shape of this organ undergoes many changes during the early 

 life of the individual, and differs much in the various genera, 

 affording thereby diagnostic characters. 1 At first a crescent, it 

 divides into a right and a left oval or disc, which either remain 

 asunder and behind the mouth (Rana, Bufo}, or they move for- 

 wards to the corners of the mouth (Hyla) or further back, and 

 unite again more or less completely, as in Discoglossus and 

 Bombinator. It is mostly of short duration, and disappears by 

 the time that the larva, by the proper development of the gills 

 and the tail and the functional mouth, changes into the tadpole. 

 But in a few species these discs transform themselves into an 

 elaborate ventral disc. Such an organ persists throughout the 

 greater part of the tadpole-stage in certain Oriental species of 

 Rana, all of which, when adult, possess fully webbed toes and 

 1 J. Thiele, Zeitschr. iviss. Zool. xlvi. 1888, p. 67. 



