102 



INTRODUCTION. 



denticulate anterior fold leads into the branchial 

 chambers (br), which contain the four branchial arches. 



Fig. 44. 



B 



Transverse section through the head of larval Pelobates fuscus. 

 (After Schulze.) A. Upper part. b. Lower part. br. Bran- 

 chial chambers, ch. Choanse. 1. Lip. m. Mouth. ph. Pharynx. 

 t. Tongue. 



These arches bear on the convex outer side the delicate 

 arborescent gills, and on the concave inner side de- 

 velop a membranous septum with vermicular perfora- 

 tions, a special sifting or filtering contrivance through 

 which the water absorbed by the mouth has to pass 

 before reaching the respiratory organs of the branchial 

 apparatus. 



Spiraculum. — The water is expelled from the bran- 

 chial chambers by one or two tubes opening by one 

 orifice in all European Batrachians. This orifice is 

 the spiraculum. In the Discoglossidae two tubes are 

 present, which gradually converge towards each other 

 at the end of the first period of development, as si i own 

 on Fig. 41, p. 98, and in the tadpole proper discharge 

 through one transverse, slit-like or crescentic opening, 

 situated in the middle of the breast (Fig. 45, a, sp.). 

 In all other tailless Batrachians the tube is single, and 



