94 The Wood-frog, Rana sylvatica LeContc. 



THE EGGS. 



Tlie eggs may be deposited near or a few feet from the edges of our 

 ponds, or in the middle of the pond (Plate i, Fig. 2n) . They are usually 

 attached to grass stems, weed stalks, twigs, brush, or rarely resting free on 

 the bottom. In this species the egg-bunches tend to be attached more 

 than in Rana pipiens. Sometimes, but rarely, we secure wood-frog and 

 meadow-frog masses on the same twig, yet they may be breeding simul- 

 taneously and in the same pond. The egg-mass at the time of laying 

 may be an inch in diameter. In the case of the mated pairs of April 

 27, 1906, and March 28, 1907, the egg-bunches measured an inch in 

 diameter just after laying. Within 2 or 3 hours the bunches had assumed 

 their normal diameters. Freshly laid masses are always very bluish in 

 tinge. The egg-bunch is globose, 1\ to 4 inches in diameter. In many 

 hundreds of wood-frog bunches, only once (April 12, 1911) have I recorded 

 the plinth form of egg-mass, as in Rana pipiens. 



The eggs are usually found in shallow water, 6 inches to 2 or 3 feet 

 deep, though occasionally egg-records have been made in greater 

 depths. Furthermore, I have found quite a pronounced tendency on 

 the part of this species to lay near the edge of the pond. As a conse- 

 quence, not infrequently in larger ponds, when very warm weather 

 follows the greater bulk of ovulation, many egg-masses are left high and 

 dry; such a condition is also not unusual in some of the smaller pools 

 in the wooded districts. A far more serious source of danger is freezing. 

 Most of the bunches are laid from | to 2 inches beneath the water's 

 surface. In many instances, long before the hatching period approaches, 

 the tops of these complements appear at the surface because of the 

 reduction of water-level by rapid evaporation. In 1907 (April 11) the 

 tops of exposed masses in two ponds were frozen in a crust of ice and 

 spoiled. The following year, on April 17, in another pond, a thin, 

 transparent crust formed, which was sufficient to kill the upper part of 

 several bunches. In all the cases observed, however, the lower portions 

 not caught within the sheet of ice have progressed nicely in development. 



The eggs of Rana sylvatica are to be confused only with those of R. 

 pipiens (Plate xx, Fig. 2) . In the former the egg-mass is globose ; in the 

 latter it is plinth-like. In R. pipiens the middle envelope is evident to 

 the naked eye, but not in R. sylvatica. The eggs of R. sylvatica are freer 

 and the outer envelope of each egg keeps its spherical form better 

 than in R. pipiens, where the eggs are closer together and have smaller 

 outer envelopes as well as vitelli. 



The outer envelope ranges from 5.2 to 9.2 mm. in diameter, rarely 

 below 5.4 mm. or above 8.0 mm.; the usual range is 5.8 to 7.0 mm.; the 

 average is 6.4 mm. The indistinct middle envelope is 3.6 to 5.8 mm. ; 

 the usual range is 3.6 to 4.4 mm.; the average is 3.8 mm.; the mode is 

 3.6 mm. The vitellus is 1.8 to 2.4 mm., rarely exceeding 2.2 mm. ; the 

 average is 1.9 mm. ; the mode is 2.0 mm. The vegetative pole is white, 

 the animal pole black or deep brownish (Text-fig. In). 



