Page:Popular Science Monthly Volume 82.djvu/52

48 at the time the report was made, while not yet sexually mature, had been living in normal surroundings for six months longer than the usual larval period. Evidently the prolongation of the larval period had an inherited effect, and the new character was apparently a dominant factor. Strangely enough no inherited effect was seen in the offspring of those tadpoles which left the water before sexual maturity. Evidently the stimulus, whatever it may be, must act on the mature germ cells to produce an effect.

Other experiments were tried on this same toad with the object of changing its peculiar instinct of caring for its young. The male, under normal conditions, plants the fertilized eggs on his back and carries them there until the embryos have reached a stage just prior to the appearance of the fore-limb buds. The tadpoles are then liberated in the water. This peculiar instinct was found to be easily modified by change of surroundings.

The combined action of heat, dryness and darkness produced an egg called by Kammerer "a giant egg." The embryo from such an egg at the time of liberation was much larger than the normal type, fully twice as large, with well-developed hind limbs. Upon leaving the water the larva produced a small adult, a change in size due apparently to lack of water in the tissues. The new form of adult laid fewer eggs, which were larger and richer in yolk. Such eggs under normal conditions produced tadpoles which, in size and form at the time of hatching, were about half way between the old type and the derived type. The new character, then, was partly inherited. The stimulus in this case clearly did not act directly on the mature germ cells, but, if the dwarf form of the adult was due to lack of water in the tissues, there may have been an indirect action on the germ cells. The effect of keeping the eggs enclosed in their envelopes on moist earth for a considerable period of time produced a type of larva called by Kammerer "a land larva." This new type when placed in the water in its usual environment appeared superficially like a water larva of the same age, but a closer examination showed that the new conditions of development on land had accelerated the growth of the lungs. The land larva had lungs with well-developed air cells, while the water larva had simple sac-like lungs. The inheritance of the newly acquired character was evident, in that the embryos of the second generation could be kept on land for a much longer period before they began to show any ill effects from their unusual environment. Thus there was, according to the author, a progressive adaptation to land life through the inherited effects of environment.

In the presence of a relatively high temperature, the mature toads were constantly in and about the water, and in the breeding season mated in the water. The egg envelopes at once swelled up, and it was