58 The Leopard-frog or Meadow-frog, Rana pipiens (Schreber). 



The egg-mass at ovulation is 1 to 2 inches in diameter. After it 

 has expanded, it is plinth-like (Plate vi, Fig. 2), the greater diameter 

 varying from 3 to 6 inches, the smaller from 2 to 3 inches. The 

 differences between the eggs of Rana pipiens and Rana sylvatica are 

 summarized under the latter. The two egg-masses can easily be sepa- 

 rated in the field by inverting the mass, thus revealing the vegetative 

 pole of each egg. In the meadow-frog the whiteness of the egg-mass 

 becomes very apparent, but in Rana sylvatica the general effect is not 

 decidedly white because of the evident encroachment of the black of 

 the animal pole on to the vegetative side. 



In Rana pipiens the outer envelope ranges from 4.2 to 6 mm. in 

 diameter, the usual range being 4.6 to 5.6 mm., the average 5.1 mm., 

 the mode 5.0 mm.; the middle envelope is from 2.3 to 3 mm., the aver- 

 age is 2.4 mm., the mode 2.4 mm.; the vitellus is 1.6 to 2 mm. in diam- 

 eter, the average is 1.7 mm., the mode 1.6 mm.; the vegetative pole is 

 white, the animal pole black or brown (Text-fig. IG). 



THE HATCHING PERIOD. 



In the field 13 to 20 days are required for hatching. In 1907, four 

 different bunches, laid at different places April 10 and 11, hatched April 

 27, May 1 and 2, i. e., 16, 21, 21, and 20 days respectively. Later in the 

 season the periods for 16 different bunches laid April 22 to May 1 were: 

 14 days for 6 bunches; 16 days for 2 bunches; 17 days for 5 bunches; and 

 18 days for 3 bunches. In 1908 two different areas gave 18 and 19 

 days at average temperatures of 51 degrees and 50 degrees. In 1910 

 one area hatched in 17 days under an average of 53 degrees, and another 

 in 14 days with an average of 55 degrees. In 1911, two different areas 

 hatched in 20 days under averages of 48 to 50 degrees. In the labora- 

 tory four different bunches of freshly deposited eggs hatched in 6 days. 

 Several bunches laid in the laboratory by mated pairs hatched in 5 or 

 6 days. It would appear that at 48 to 51 degrees they hatch in 20 to 

 18 days, at 53 to 55 degrees in 17 to 14 days, at 55 to 65 degrees in 14 

 to 7 days, at 65 to 75 degrees in 7 to 4 or 5 days. 



THE MATURE TADPOLE. 



Length of the body 1.3 to 2.2 in the length of the tail, average 1.7. 

 Width of the body in its own length 1.4 to 1.7, average 1.5. Nostril 

 1.1 to 1.5 (average 1.3) nearer the eye than the end of the snout. 

 Eye is 1.1 to 1.3 nearer the spiracle than the snout. Distance between 

 nostrils in the interorbital space 1.5 to 2.2, average 1.8, seldom over 

 2.0; in mouth, 1.1 to 1.5, average 1.25. Spiracle sinistral, 1.25 to 1.7 

 nearer the base of the hind legs than the end of the snout, average 1.5, 

 rarely reaching 1.7 or under 1.35. Anus dextral. Depth of tail in its 

 own length 2.7 to 3.4, average 3.0. Depth of muscular portion of tail 

 in depth of tail 1.6 to 2.4, average 1.9. Mouth contained in interorbital 



