A third series of experiments was tried on two European salamanders, Salamandra ater and Salamandra maculosa. The former is a black mountain salamander which has the peculiar habit of bringing forth its young alive, always a brood of two with lungs already functional. The embryos pass through their early development in the body of the mother, nourished by the yolk of eggs that fail to develop. Salamandra maculosa is a yellow-spotted salamander of the lowlands which lays its eggs in running brooks. When kept away from the water the female of the spotted salamander at first dropped her eggs on the ground directly after fertilization. Such eggs failed to develop. In the course of two years, however, this salamander gradually acquired the habit of holding the eggs in the body for several weeks. The eggs became fewer in number and larger in size until the young were brought forth alive in a condition like that of the black salamander. Females of the latter were treated in an exactly opposite way. They were kept in or near the water until they acquired the habits of the spotted salamander. Inheritance was imperfect in each case. The new type of spotted salamander, under the usual normal conditions, deposited in the water a brood of five fairly well developed young. The new type of black salamander, under normal conditions, deposited in the water a brood of three young in a stage of development more advanced than that of the spotted salamander. When the artificial conditions of the experiments were continued through two generations the effect was greater. The author claims that his experiments show the inheritance of acquired characters influencing structure and instinct.
A second experiment was tried on Salamandra maculosa to test the inheritance of acquired color due to change of background. A brood of young salamanders was divided into two lots, one of which was kept for six years on a background of yellow, the other on a background of black. The former showed a decided increase in yellow markings, the latter an increase in black markings. The young of the yellow type were allowed to begin their development on a background of neutral tint, but before reaching maturity the brood was divided as before into two parts and placed, one part on a yellow background, the other on a black background. The set on yellow, after two years, showed a great increase of the yellow markings as compared with their parents, in fact the yellow pigment nearly covered the body. The set on the black background showed more black than their parents, but less black than the previous set similarly treated but of normal parents. These experiments, according to the author, show the progressive effect of environment in the inheritance of acquired colors.
The evidence presented by these experiments, which have been briefly described in the preceding paragraphs, should be considered in
