The Eastern Wood Frog 



(Figs. 246 and 247.) The masses may be attached to twigs and 

 grasses in shallow water, or they may be free. 



After the eggs have been in the water a week or more, the 

 mass flattens and spreads greatly, and rests on the surface of 

 the water. There are likely to be several masses close together 

 in the water. The jelly about the eggs becomes green in colour, 

 and thus the egg-masses bear a close resemblance in position and 

 appearance to the floating masses of green pond-scum. The 

 green colour of the jelly about the eggs is due to the presence of 

 innumerable microscopically small green plants. The relation 

 between these plants and the developing egg is one of mutual 

 advantage. The plants feed upon the large amount of carbon 

 dioxide breathed out by the young tadpoles, and the tadpoles 

 get, as their share in the partnership, the free oxygen that the 

 plants give out as a waste product from their starch-forming 

 process. This oxygen must be of infinite value, produced every- 

 where in the midst ot the egg-mass, because it supplies sufficient 

 pure air for breathing, in spite of the crowded condition of the 

 two thousand or more growing tadpoles. 



These egg-masses are not easily found, partly because they 

 are so inconspicuous, and partly because our attention is rivetted 

 on the very conspicuous jelly masses (Fig. 249) of the spotted 

 salamanders, 1 or of the marbled salamanders 1 (which choose the 

 same time and often the same place for depositing eggs). Eggs 

 that are laid in water that afterwards freezes are not killed, 

 and will develop as soon as a higher temperature returns. 



As has been said, the hoarse croaking of the Wood Frog is 

 heard only at the breeding-season. At that time, however, 

 dozens of the frogs croak together in a most clamorous fashion. 

 The repeated notes are low-pitched (about an octave below 

 middle C). The notes have 

 been compared to the quack- 

 ing of ducks, but near at 

 hand, at least, they are much 

 less unmusical. The males alone do the croaking. They have 

 no external vocal pouches, but, as in the Pickerel and Green frogs 

 the throat and sides of the body over the lungs distend consider- 

 ably as the sounds are produced. The breeding-season is likely to 



r 



1 Amblystoma punctatum or Amblysloma opacum. 



209 



