DEVELOPMENT OF THE BLOOD VESSELS IN THE FROG. 253 



The limbs are well developed; the hind limbs when fully extended 

 reaching a little beyond the end of the tail ; the toes are well formed 

 and webbed. The fore limb of the left side projects through the 

 opercular spout ; that of the right side is protruded through the 

 opercular fold, in which it forms a ragged hole. In slightly 

 younger specimens the right fore limb still lies within the opercular 

 cavity. 



The mouth has changed its appearance altogether : the horny 

 jaws and frilled lips of the tadpole have gone, and the mouth 

 aperture is now slit-like and shaped as in the adult frog, though not 

 extending so far back. 



2. Internal Anatomy. 



A well-developed tongue is present, attached to the floor of the 

 anterior part of the mouth, and with its tip bifid and directed back- 

 wards as in the adult. 



The gill arches and gills are still present, and are arranged very 

 much as in the earlier stage. Velar folds of the floor of the 

 pharynx are present, overlapping the gills, but are somewhat smaller 

 than before. The filters are exceedingly complicated and well 

 developed, but the gill tufts themselves are, relatively to the bulk of 

 the animal, much smaller than before. 



The alimentary canal behind the pharynx has proportions much 

 closer to those of the adult than it had in the earlier stages. The 

 stomach is more dilated than before, and has the adult shape and 

 position : the small intestine has shortened considerably : the liver 

 is large, and the gall bladder, which lies on the right side, behind 

 the right lobe of the liver, is of relatively enormous size. 



The head kidneys are very much reduced in size, and are now 

 relatively insignificant bodies, in which, however, the hindermost of 

 the three nephrostomies on each side are still present. The glomerulus 

 is still present, having the same appearance and relations as in the 

 earlier stages, but is of distinctly smaller size. The Wolffian 

 bodies are large, especially at their hinder ends. The reproductive 

 organs, showing as yet no difference of sex, are present as a pair 

 of narrow longitudinal bands lying ventral to the Wolffian bodies, 

 and along the inner borders of their anterior halves. The fat-bodies 

 are present, in close connection with the anterior ends of tho repro- 



