796 MR EDWARD J. BLES ON THE 
to be established is to bring the water into such a state that the larvee will find their 
food when it is required. This condition will be explained later (pp. 813-14). 
By carrying out such measures I obtained from one female between April and July 
1903 more than fifteen thousand eggs. Of these, twelve thousand were taken out of 
the aquarium and counted, and the remainder were estimated at three to five thousand. 
Some general significance may, I believe, be attached to the results in breeding this 
frog, the more so as they are in accordance with other similar results obtained by 
SEMPER (1878) with Axolotls and by myself with Axolotls, Triton waltliu, and Dis- 
coglossus.* SEMPER showed that by feeding them copiously, and by keeping Axolotls 
crowded together in small vessels, he could obtain spawn from the same individual three 
or even four times a year after a sudden transference to an aquarium stocked with 
growing plants, with stones on the bottom and supplied with running water. I have 
repeated his experiments and can fully confirm his statements. With Dviscoglossus 
pictus | have had a similar experience. Specimens kept ina small vivarium for four 
and six years have been given a superabundance of food during the summer, allowed 
to hibernate, and, when they showed signs of readiness to breed, a little tank in a 
corner of the vivarium has been filled with suitable pond water, and invariably within 
forty-eight hours the frogs have spawned. On two occasions the males have taken to 
the water in the spring and assumed their nuptial characters, but for several weeks the 
water which had stood in the tank during the winter has been allowed to stand. No 
pairing took place, but as soon as the water was changed spawn was deposited in 
twenty-four hours. Two female Discoglossus have each spawned twice every summer 
for the last three years, just as they do when free. Two pairs of Triton waltliz, which I 
have reared from larvee, have spawned when two years old. In their case the same treat- 
ment was carried out. They were well fed in the summer, kept cold in the winter, and 
fresh water added to the aquarium when they showed readiness to pair. 
These various experiences appear to indicate that the difficulty met with in 
breeding Amphibia kept in confinement is not due to any toxic influence on the 
gonads due to the results of close confinement. Darwin was inclined to believe 
that the functions of the generative organs were sometimes impaired by captivity, 
but unless and until concrete evidence is given to show what specific influence 
is at work, it would very often be simpler to assume that the external conditions are 
unfavourable for breeding, or deficient. 
In the case of Xenopus all the other conditions may be present, but if there is 
no daily change of the water there is no oviposition, and although the male may 
embrace the female, the behaviour of the latter clearly shows that she is not 
ready to spawn. 
If the view is correct that breeding is brought about in animals, especially in 
those with a fixed breeding season, as the response to a certain set of definite 
external stimuli on the sexually mature of the species, it may help to explain 
* And also by P. Kammerer (’04) with Salamandra maeulosa and S. atra. 
