1908-9. ] THE HaBITs OF PLETHODON CINEREUS ERYTHRONOTUS. 487 
among Urodeles—does along the lines mentioned actively promote the 
welfare of her brood. 
In those last mentioned and in other experiments in which the clusters 
of eggs were entirely immersed in running water it was noticeable that 
the mucous envelopes would imbibe readily a small quantity of ‘water 
and swell slightly in consequence, but the limit to this process was usually 
reached within the first half hour, nor did any second period of imbibition 
occur. No softening of the envelopes was to be noted even after constant 
immersion for three weeks. These qualities of the mucus mark it as 
different from that of most amphibian spawn which continues to absorb 
water and to soften until the larve escape. They probably are to be 
considered adaptations to prevent rains of even most unusual duration 
from softening the mucus and turning loose the larve prematurely. 
The bottle method before described was used to test the possible 
effect of light upon development. Several bunches were exposed to 
daylight, which however never became direct sunlight, while others of 
the same stage of development were kept in entire darkness as controls, 
the temperature being in each case, within limits of variation of three 
or four degrees, the same. At the end of twenty-five days no difference 
in the degree of development of the two lots was to be detected. The 
lack of pigment in the egg might be put forward but the whole expla- 
nation cannot rest on this for early in the life of the larva pigment appears 
in the skin and rapidly increases in amount; and in the experiment this 
pigment was present for the last twenty days. In the experiments of 
various investigators to determine the effect of light upon growth Am- 
phibian larve in aquaria have frequently been used; in which case the 
oxygen and part of the food have been derived from the water. Since 
both these things would be more abundant in the better lighted aquaria, 
factors must be allowed for, whose exact influence is unknown. In the 
present case the food and oxygen factors are the same for both sets 
of larve and the uncertainty of result due to several factors varying 
simultaneously is lacking. 
PoInts ARISING OuT OF THE LUNGLESS CONDITION. 
In Amphibia generally the function of the skin as an organ of respira- 
tion accessory to the lungs has long been recognized. Later Maurer 
(’98) drew attention to the advantageous position for purposes of respira- 
tion held by the capillaries of the bucco-pharynx, many of them being 
situated in the epithelium itself. To these localities therefore the atten- 
tion of investigators was naturally directed in seeking the means which 
