34 



BERTRAM G. SMITH. 



yolk sac is reduced enough so that the larva no longer lies on 

 one side. The mouth opening is now only slightly ventral. 

 Pigmentation is greatly advanced, and extends to the external 

 gills ; when viewed from above the larva is now nearly black. 

 The ventral side remains white and nearly transparent in the 

 throat region and yellow in the region of the abdomen or yolk 

 sac. The heart is still visible, and the course of the blood through 

 it maybe readily followed. The vitelline vein, now lying almost 

 in the median line ventrally, shows signs of degeneration. 



P'ig. 10. Fig. ii. 



Figs, io and n. Photographs from living material, showing early stages in the 

 development of the larvae of Cryptobranchus allegheniensis. Natural size. 

 Fig. io. Larvae one month after hatching. Length 35 mm. 

 Fig. 11. Larva ten weeks after hatching. Length 40 mm. 



At this age the larvae are more active swimmers than the 

 adults. The front limbs assist in starting by a quick simultaneous 

 backward stroke. 



Ciliation of the epidermis is now found only on the gills, where 

 a strong eddying current of water is produced. No water current 

 in at the mouth or nares and out through the gill slits could be 

 detected. 



At this stage shedding of the cuticle was observed for the first 

 time, and was quite general ; the water of the aquaria became 

 cloudy with portions of detached epidermis. 



Ten Weeks' Larva. — (See Fig. 1 1.) There is a slight increase 

 in length since the first month ; the larvae now range from 35-40 

 mm. The limbs are better developed, possess the full number 

 of toes, and are used in walking in the same manner as in the 

 adults. The limbs are broad and flat, and are used as paddles 

 in swimming at a moderate rate of speed. After fixation the 

 somites show very distinctly. 



