132 



THE BOOK OF NATURE STUDY 



gill-cover, a gill-chamber, gill-arches, and gill-filaments, but 

 neither the gill-cover nor the gill-filaments of the tadpole are 

 exactly equivalent to those of the ordinary fish. There is a great 

 change in the mouth; it now has horny jaws, and the lips have 

 many minute horny teeth, each a single cell like a nightcap in 

 shape, replaced by others beneath them as they get worn off. 

 The animal is able to swim about actively, and the crescent- 

 shaped cement gland, after dividing into two widely separated 

 circular discs, disappears. In regard to this short-lived organ, it 

 may be noted that the term " sucker," often applied to it, is 

 inappropriate, since there is no muscular adhesive action. The 

 general change in shape is noteworthy, for after the gill-covering 

 fold fuses with the skin behind (leaving only the spiracle open) the 

 head ceases to be distinct from the body. The tadpole is now 

 feeding upon larger booty, e.g. small insect larvae and small worms, 

 as well as pieces of plants, and the intestine is very long. It may 

 be seen through the skin, coiled up like a watch-spring. At this 

 stage the tadpoles in the aquarium may be fed on small quantities 

 of mixed meat, on grated yolk of egg, and the like ; but care 

 must be taken to avoid fouling the water by putting in too 

 abundant supplies. 



The Second Tadpole Stage. The hind-limbs bud out at the 

 root of the tail The fore-limbs start at the same time, but 



FlG. 44. The second tadpole stage, 

 nearly twice the natural size, show- 

 ing the growing hind-leg (HL), the 

 cloacal opening (A), the zigzag 

 connective - tissue partitions be- 

 tween the muscle-segments in the 

 tail, the bulging gill-chamber, etc. 

 (After A. Milnes Marshall.) 



FlG. 45. A later stage before the beginning of the 

 metamorphosis. The hind-legs have grown 

 considerably. The elbow of the fore-limb is 

 projecting through the transparent gill-cover 

 (o), in which a hole will soon be broken. It 

 will be seen that the mouth has still its 

 rounded suctorial character. (After A. Milnes 

 Marshall.) 



are retained within the gill-chamber until they are fully formed, 

 when the right one breaks through the skin and the left one 

 gets through the spiracle. In front of each limb there is a small 



