LIFE-HISTORY OF XEHNOPUS LAVIS, DAUD. 795 
burner is very convenient, as the temperature of the aquarium remains constant some- 
times for weeks together, and a variation of a degree can be put right by slightly 
lowering or increasing the flame. Between the bottom of the aquarium and the flange 
of the water-bath I have a coil of three turns of asbestos cord, which keeps the glass 
away from the hot metal, and prevents evaporation from the water-bath. 
In such aquaria my Xenopus have now lived for years, and in them they have 
spawned, and the tadpoles been reared, in one case to maturity. 
The bottom of the aquarium is covered with earth and stones, and Vallisnerva 
thrives in it. During the summer the Xenopus are kept at about 25° C., and the 
temperature may rise occasionally to 28°-30° C. They are fed daily with small earth- 
worms or thin strips of raw calves’ liver, and are fed until they refuse to eat more, 
which they do in a comical manner, by pushing aside the food with the palm of the 
hand when it is held near them. ‘The water in the aquarium is never changed. 
In December the temperature is allowed to sink to 15°-16° C. during the day, 
and it may sink to 5°-8° during the night. The frogs then become lethargic and torpid, 
take no food for days, eat very little at a time and move about rarely, spending very 
little time, at any rate during the day, at the surface of the water. I have on a few 
occasions approached the aquarium very quietly and found one or the other of the 
frogs lying flat on the stones with what appeared to be a translucent film dimming 
the brightness of its eye. 
A sudden noise, however slight, makes the frog start up, and the film moves slowly 
outwards and forwards, uncovering the eye, and is recognised as the lower eyelid. The 
frog then moves away. Judging from analogy, one might conclude that the frog had 
been aroused out of its sleep. Whether this conclusion is justified or not, the facts 
seem worth recording, as the evidence of the occurrence of sleep in the lower vertebrates 
is somewhat slender. 
When the temperature of the aquarium rises in the spring and the days become 
brighter, a change in the behaviour of the frogs becomes evident. The female and males 
spend a great part of the day at the surface of the water with eyes and nostrils above the 
surface. The males become exceedingly restless, swimming about with an air of wishing 
to escape from the aquarium. Both sexes are now very shy, and difficult to feed. 
There may or may not already be attempts at pairing, but by taking the 
following measures pairing will take place immediately (with or without spawning), or 
at least the male, after being silent the whole winter, will commence to croak at once. 
First, the temperature of the aquarium is raised to 22° C. and, secondly, when it has 
become constant, a certain amount of the water, say 2 gallons, is drawn off morning 
and evening, allowed to cool for twelve hours, and then run in slowly in the following 
manner, in order to simulate the fall of rain. The cooling vessel is raised above the 
level of the aquarium, and a syphon is used to run off the water. The lower end of 
the syphon is drawn out to a fine point, and turned up in such a way that the water 
rises up like from a fountain, and falls as spray into the aquarium. The third condition 
