32 The American Toad, Bufo lentiginosus americanus LeConte. 



every case they eventual!}' drop to the level of all the eggs previously 

 laid. After each period of emission the female moves, thus getting the 

 eggs out of the way; and this doubtless facilitates the fertilization of the 

 next mass of eggs. The period of rest is seldom less than 1 or 2 minutes, 

 and often several minutes elapse between periods of sexual activity. 

 When a pair lays from 4,000 to 7,000 eggs two strings, each 20 or more 

 feet long it is easily seen that the egg-laying generally extends over 2 

 or 3 hours or more. An actual count of the eggs taken from one ovary 

 of a mature female captured April 28, 1905, gave 2,356 ripe eggs. 



THE EGGS. 



The eggs are laid ordinarily in quiet water; it may be shallow, but 

 not always so. The eggs are found in pools and ponds, artificial or 

 natural, in marshes, back-waters, ditches, etc. The strings (Plate vn, 

 Fig. 2; Plate i, Fig. 2e) rest merely on the bottom or are twined about 

 vegetation or sticks which happen to be near at hand. 



The eggs (Text-figure IA) are laid in long spiral tubes of jelly. The 

 vitellus varies from 1.0 to 1.4 mm. in diameter; 1.2 mm. is the modal 

 diameter; the average is 1.1 mm. Each individual vitellus has a quad- 

 rangular envelope (Text-figure IA), which has two of its sides parallel 

 with and closely apposed to the inner tube of jelly. These individual 

 envelopes abut and are inclosed within the inner tube, which varies in 

 diameter from 1.6 to 2.2 mm. This inner tube is in turn incased in an 

 outer tube of jelly. The latter may range from 3.4 to 4.0 mm. in 

 diameter. 



THE HATCHING PERIOD. 



The hatching period is usually very short. In 1907 a few of the 

 records are as follows: On May 14 and 15 myriads were laying in one 

 place, and by May 18 all of the eggs were hatched; in another place, 

 eggs laid May 14 at 10 a. m. were hatched by 10 a. m., May 17; some 

 eggs laid earlier in the season (April 30) hatched in 5 days. In 1908 eggs 

 laid April 25 hatched in 10 days when the maximum air-temperatures 

 averaged 60 degrees. In 1910 the species began laying very early in 

 April. On April 5 in one place it began when the air-temperature 

 reached 81 degrees, but the eggs did not hatch until 10 days later, under 

 an average of 57 degrees air-maxima. In another place, under quite 

 different conditions, they hatched in 12 days. In 1911, in one locality 

 they hatched in 5 days when the maximum water-temperatures averaged 

 71 degrees and when the maximum air-temperatures averaged 73 

 degrees. In another instance, they hatched in 9 days when the water 

 averaged 62 degrees and the air averaged 65 degrees. The eggs are 

 usually in shallow water which is quite responsive to air-temperatures. 



In general, when the eggs are subjected to 70 degrees or more they 

 hatch in 5 to 3 days; from 65 to 70 degrees, in 8 to 5 days: from. 55 to 

 65 degrees in 12 to 8 days. 



