BAN A. 311 



tadpoles are still to be found in August, and are even 

 sometimes compelled to hibernate in that condition. 



Many observers who have kept pairing frogs of 

 this species in confinement have been disappointed at 

 findiuo- the e°'o\s laid under these conditions to be 

 unfertilised, this being often the case when single 

 pairs are confined in jars, and apparently due to the 

 male not emitting his fecundating fluid at the rigdit 

 moment. Fischer-Sigwart has recently attempted to 

 explain this fact by suggesting that the males fecundate 

 the eggs some time after they are laid and after the 

 release of the females from embrace. I cannot accept 

 this explanation, because I have observed, in prac- 

 tising artificial insemination, that the spermatozoa 

 appear to be unable to penetrate the eggs after the 

 mucilaginous capsules have become swollen out with 

 water, which takes place very rapidly after deposition. 

 In order to fully satisfy my mind on this point, I 

 made this spring (March 22nd) the following experi- 

 ment. 



At 11 a.m. I pressed into two dishes filled with 

 water from the supply- tap a few eggs (about fifty in 

 each dish) from a female held in embrace. The pair 

 were then separated and kept dry until 2 p.m., when 

 the male was killed and the fluid removed from the 

 vesicula seminis, whilst two further small lots of eggs 

 were pressed out of the female into the dishes in 

 which lay those previously obtained, with their cap- 

 sules now considerably inflated. I then poured the 

 seminal fluid, diluted in a wineglassful of water, over 

 the four clumps of eggs. The result was the same in 

 both dishes : the eggs laid at 11 a.m. and fecundated 

 at 2 p.m. did not develop (with one and two excep- 

 tions respectively), whilst the great majority of the 

 others underwent their normal evolution. 



Eggs. — Vitellus measuring 2 to 3 mm. in diameter, 

 black, with a small white or grey spot on the lower 

 pole; mucilaginous envelop measuring 8 to 10 mm. 

 in diameter. The eggs form one or two large balls, 



