TADPOLES. 



105 



and Alytes obstetricans, in which these organs are 

 represented by dotted lines. In addition to these 

 lines, all tadpoles show more or less distinctly a small 

 whitish gland in the middle of the head between the 

 eyes, the so-called frontal gland or pineal gland, which 

 in earty stages is connected with the brain. A glan- 

 dular streak extending from the nostril towards the 

 eye is the lachrymal canal. 



The presence of a number of pulsating lymph-sacs 

 has lately been discovered by Weliky on each side of 

 the dorsal caudal crest. 



Pigmentary Network. — In addition to the ordinary 

 pigment-cells, the tadpoles of afew genera (Discoglossus, 

 Bombinator, Pelodytes) present a system of fine black 

 lines, most apparent on the caudal crests and the more 

 feebly pigmented parts of the body, which afford 

 excellent characters for their identification. It is a 

 fact worthy of notice that when the end of the tail has 

 been injured these pigmentary lines are not reproduced 

 on the regenerated portion. Their aspect is shown in 

 the following figures (from 'P. Z. S.,' 1891), repre- 

 senting much-enlarged pieces of the upper caudal 

 crest of Pelodytes (a) and Discnglossus (b). 



Fig. 47. 



The following key has been drawn up to facilitate 

 the identification of the genera and species in the tad- 

 pole condition. 



I. Spiraculum median ; anus median ; tail rounded 

 or obtuse at the end ; a papillose edge all round 



