530 BERTRAM G. SMITH 



In the free-swimming larva, the heart beats more rapidly than 

 was the case during embryonic development. 



Within a week or two after hatching, the rapid growth of the front 

 limb rudiments enables the larva to support itself in the normal 

 position of the adult. One month after hatching, the front limbs 

 have increased decidedly in length and possess the full number 

 of digits (four) . The form and position of the front limbs adapt 

 them for use as paddles ; by means of a simultaneous backward 

 stroke they aid the larva in getting a quick start for swimming. 

 The posterior limbs develop more slowly; at this time they are 

 relatively short and as a rule possess but three digits, though in 

 some cases the full number (five) are present. Ten weeks after 

 hatching in all cases both pairs of limbs possess the full number 

 of digits and are used in walking in the same manner as in the 

 adult. The limbs are broad and flat, and in swimming at a 

 moderate rate of speed are used as paddles. After the sixth month 

 of larval development the posterior limbs surpass the anterior in 

 size and strength. In the two-year-old specimens reared in the 

 laboratory the limbs appeared weak and poorly developed as com- 

 pared with newly captured specimens of the same age. 



As in the adult, the tail is the principal organ of locomotion 

 during rapid swimming. Up to five or six months after hatching 

 the tail remains much larger in proportion to body-size than in 

 the adult. In the year-old larva the tail is proportionally much 

 smaller than in specimens ten weeks after hatching. In the 

 two-year-old specimens reared in the laboratory the tail is smaller 

 than in newly-captured specimens of the same age. 



'One month after hatching, pigmentation is greatly advanced 

 and extends over the external gills; when viewed from above 

 the larva is now nearly black. The ventral surface remains 

 white and nearly transparent in the throat region, yellow in the 

 region of the yolk sac. Six months after hatching, the dorsal 

 surface shows large dark spots of unusually dense pigment, which 

 are characteristic of all the later stages; the ventral surface is 

 slightly pigmented. In the year-old larva, the dorsal surface 

 is still nearly black, but with a few scattering inconspicuous 

 yellow spots; the abdomen is grayish and the throat region almost 



