20 General Account of the Ithacan Anura. 



in the latter group the average is from 33 to 53 imn. Besides, the vitelli 

 of the former are larger in proportion to the size of the adults than in 

 the two latter. In the three species of Rana with short larval periods 

 the vitelline diameters extend from 1.6 to 2.4 mm., while those of the 

 larger Rana clamata and Rana catesbeiana, with long larval periods, are 

 only 1.2 to 1.7 mm., little more than the vitelli of the two species of Hyla. 

 If Chorophilus triseriatus with a body-length of 1 inch and an egg-vitellus 

 of 1 mm. be considered as the unit, the ratio of body-length to size of 

 vitellus in our eight species will be as follows : 



Chorophilus triseriatus 1 .00 | Bufo 1. americanus 0.60^ 



Rana sylvatica 1 .00 Rana pipiens 56 



Hyla pickeringii 80 Rana clamata 48 



Hyla versicolor 75 Rana catesbeiana 20 



Rana palustris 64 I 



Except for the wood-frog, the series begins with the smallest and pro- 

 ceeds nicely in order of adult size to the largest, namely, the bullfrog. 

 The eggs of this species are proportionately only one-fourth or one-fifth 

 of the size attained by the three members of the Hylidae. The surprise in 

 the comparison is that the wood-frog's egg is proportionately five times 

 that of the bullfrog and almost twice that of its other three congeners. 



Thus, we see that the relative smallness of the eggs, the late deposition 

 of the eggs, and the greater transformation-size required — all combine 

 to make the green-frogs and the bullfrogs spend one or more winters in 

 the larval stage. 



Among the species with short larval periods there is considerable 

 difference. The true larval periods of the toad, the tree-toad, and the 

 wood-frog may be one-half that of the other three. The last species, 

 namely Rana sylvatica, may at some seasons occupy just as long a 

 period as the meadow-frog, the peeper, or the pickerel-frog. 



THE MATURE TADPOLES.* 



As mature tadpoles, we have chosen specimens which correspond to 

 the third period of Duges (beginning of the budding of the hind limbs). 

 This makes our tadpoles comparable to Boulenger's descriptions of 

 European forms. We have employed the same terms which he has 

 well defined. In one particular we have departed from his plan. The 

 upper labial teeth have been numbered from the outer edge of the lip 

 to the inner row nearest the beak and the lower labial teeth from the 

 row nearest the beak to the outer one next the papillose border. This 

 is the vertical order in which they appear when the mouth is flattened 

 out for examination. Furthermore, in our eight species, there is a 

 tendency for reduction to take place in the upper labial row or rows 

 nearest the beak and in the lower labial row or rows nearest the border. 



*Cf. Hinckley, Mary. On some Differences in the Mouth Structure of Tadpoles of 

 Anurous Batrachians found in Milton, Massachusetts. Proc, Bost. Soc. Nat. Hist., vol. 

 XXI, pp. 307-314. 



