Hylid£e 



their more slender shape and by the more lateral position of the 

 eyes. By April 20th the legs are budded. The tadpoles are now 

 one-half inch long, are black in colour, finely dotted with gold, and 

 with the underparts very brilliantly copper-tinted.' 



The final transformations take place from May 26th to June 

 1 2th, when the tadpole is slightly over an inch long.* The front 

 legs appear, the tees furnished with their small disks. The stripes 

 on the back do not appear until the creatures are actually on the 

 point of leaving the water. Since the feet are so slightly webbed, 

 the young frogs are very poor swimmers and are drowned unless 

 they have opportunity to leave the water. 



The young frogs are extremely delicate and timid. They 

 look like the full-grown tree frogs, except that they are only one- 

 half inch in length. They hide at once under convenient leaves, 

 sticks, and stones about their marsh. 



The genus Chorophilus is not found outside of the American 

 region. It represents a tree frog that has sufi'ered much retro- 

 gression in the structures for arboreal and aquatic life. The 

 adhesive disks are ineffective because of their small size, and the 

 toes are scarcely webbed. The species nigriius presents great 

 variation in the different parts of the country. So great is the 

 variation that four forms are easily distinguished, namely: 

 nigritus Le Conte of the Southeast, jeriarum Baird of the 

 East, triseriatus Wied of the West and Southwest, and septen- 

 trionalis Stejneger, found at the extreme North, in the middle part 

 of the continent (Manitoba and the Hudson Bay region). Nigri- 

 ius and jeriarum differ mainly in the relative lengths of the head. 

 The great difference between these two forms and the other two 

 (namely, triseriatus and septentrionalis) lies in the measurement 

 of the hind legs; those at the South and East have legs that meas- 

 ure the longest, those at the North show an unusually short leg 

 measurement, and triseriatus is intermediate in this characteristic. 



' These tadpoles may be identified by a careful examination of the mouth; tlie upper lip has 

 two rows of teeth, the lower has three. The teeth are notched at their tips. The border of the lower 

 lip is not doubled in at the angles of the mouth. 



i The main facts of the development are from the account by O. F. Hay (Amer. Nat., vol. 23). 



160 



