34 DEVELOPMENT AND LIFE-HISTORY 



Biology," by Huxley and Martin, it is stated, p. 163, that "the 

 animal (tadpole) crops the aquatic plants on which it lives by 

 means of the horny plates with which its jaws are provided." 

 Again, p. 164 : — "The labial membrane and the horny armature 

 of the mouth disappear, while teeth are developed in the upper 

 jaw on the vomers ; the intestine becomes less and less coiled, as, 

 not growing at the same rate as the body, it becomes relatively 

 shorter, and the animal gradually changes its diet from vegetable 

 to animal matters, the perfect frog being insectivorous. This 

 statement appears to be that generally adopted as fact at the 

 present day, and it was in hopes of throwing some light on these 

 apparently contradictory statements that my observations and 

 experiments were first commenced. 



The ova or frog-spawn is deposited in water early in the year. 

 From the first or second week in February to the second week in 

 March, according to the season, the male and female frogs repair 

 to any fairly shallow, stagnant, or semi-stagnant pool, and there 

 the spawn is deposited in large masses, fertilisation taking place as 

 the ova are being deposited in the water. When we consider the 

 immense numbers of ova deposited by one female, and that each 

 egg is surrounded by a membrane which rapidly swells when it 

 touches the water into a semi-gelatinous covering, it appears 

 astonishing that nearly every egg becomes fertilised. Out of a 

 mass which, when fully swollen by absorption of water, measures 

 from six to nine inches in diameter and contains hundreds of 

 eggs, not more than ten or twelve eggs will remain undeveloped. 

 The further development of the egg is, however, much dependent 

 on temperature. During the present season (1887), thousands 

 around Bath were killed by the severe cold, which occurred within 

 a few days of spawning. 



The eggs were laid in some of the ponds this year about 

 February 27th. Cold weather set in within a day or two, and 

 from March 12th to March 21st intense frost and deep snow ])re- 

 vailed, so that after the snow had disappeared masses of dead 

 spawn were taken from the same pond as that from which some 

 hundreds of tadpoles had by this time developed from the spawn, 

 which had been kept in a room at a minimum temperature of 

 40° F. and a maximum of 55" I*'. 



