HABITS OF CRYPTOBRANCHUS ALLEGHENIENSIS. 33 



vein is very prominent. The anterior limb rudiment is provided 

 with two toes. The somites are plainly visible in most speci- 

 mens, but do not show in the figure. The mouth opening is large 

 and ventrally situated, and the mouth cavity is well developed. 

 The eyes are more prominent than in the adult. The dorsal and 

 lateral surfaces, especially of the head, are thickly studded with 

 small round white spots, presumably sense organs and mucus 

 glands. 



On account of the large yolk sac, the larva habitually lies on 

 its side, turning occasionally from one side to the other. When 

 the larva is placed upon its back, the righting reaction, aided as 

 it is by the ballast of yolk, is very quick. The newly hatched 

 larva is able to swim rapidly in a straight line for a short distance, 

 using the tail as a propeller. 



The larvae avoid the light and are positively rheotactic. 

 Under natural conditions, the result of these two modes of 

 behavior probably is that the larvae remain in the nest. 



Aeration of the blood is afforded, not only by the external 

 gills, but by the capillaries which lie close to the surface all over 

 the body. The tail may be of especial importance in respiration, 

 for here, as in the external gills, the capillary network lies in close 

 proximity to the water on both sides. 



At the time of hatching, patches of cilia are scattered over 

 practically the entire surface of the body, but are especially 

 numerous on the gills. Their beat is backward, and they create 

 a current of water, subservient to respiration, which is particularly 

 strong in the vicinity of the gills. The presence of cilia on the 

 ectoderm of Amphibian embryos has been remarked by various 

 writers (see Assheton, '96). 



The Month-old Larva. — In larvae about a month after hatch- 

 ing (see Fig. 10), there was noted a marked increase in length, 

 principally due to the development of the tail. The larvae now 

 measure from 30 to 35 mm. There is also a rapid elongation 

 and development of the front limbs, which now have four toes. 

 The form and position of the front limbs adapt them for use as 

 paddles. The posterior limbs develop more slowly, are relatively 

 short and have but three toes distinctly visible, though in some 

 cases rudiments of the fourth and even the fifth are present. The 



