41 8 ZOOLOGY FOR MEDICAL STUDENTS chap, xi 



consequently they cannot stand an absolutely dry atmosphere. And 

 they still possess a larval stage, fish-like in structure, which inhabits the 

 water.i In the Urodele the larva presents a striking resemblance to a 

 young Lepidosiren or Protopterus and is provided with external gills 

 belonging to visceral arches III, IV and V. In the Anura the larva is 

 a " Tadpole," the body from the anus forwards being greatly broadened. 

 This broadening of the body is associated with the great length of the 

 spirally coiled intestine. 



Parallel to the edge of the mouth the tadpole normally possesses a 

 number of fine-toothed oral combs which it uses for fraying out its food. 

 Each tooth of the comb is built up of a series of hollow cones fitting into 

 one another, each cone being a comified cell. Each column of cones is 

 constantly being added to at its base to make up for the loss of the 

 apical cone which is shed when worn out. The teeth of the innermost 

 row, along the margin of the mouth, are bigger and stronger than the 

 others and instead of being spread apart they are in contact and fused 

 together so as to form a horny beak. 



1 Various anurous amphibians have developed interesting arrangements 

 whereby this particular difficulty — the need for an aquatic environment 

 during early stages — has been more or less completely circumvented. A 

 short account of these will pe found in the writer's Embryology. 



BOOK FOR FURTHER STUDY 

 Gadow. The Cambridge Natural History, Vol. VIII. 



