Two letters of Charles Darwin, on "Worms and their Habits,"
C.
Exhibited by Professor von Gruber.
Experiments by P. Kammerer on changes produced in the colours in the skin of the Fire Salamander—Salamandra maculosa—by keeping them on yellow or black earth respectively.
According as to whether the animals are kept on yellow or black earth the yellow or black colouring of the skin spreads, and this change of colour appears in the same way in the offspring, though a direct influence of the colour of the earth on the germ plasm is absolutely unthinkable. The two pictures in the lower part of Figure C 1 show the colouring of that generation to which the animal portrayed above belongs, according as to whether they have been kept permanently on yellow soil (right) or returned again to black soil (left). Here, it is true, it is not a question of a new quality or tendency. The capacity in the parents to deposit black pigment in their skin has been increased or decreased according to their surroundings. But the distinctive point remains, that their offspring is subsequently endowed with the inherited tendency to produce proportionately more or less pigment. This may, however, be a direct result of the abnormal life conditions of the parents, in so far as the depositing of more or less pigment in the skin of the parents is certainly not a purely local process, but rather is bound up with other metabolic changes which may extend to or influence the developing gametes.
Very remarkable are the hereditary changes which Kammerer established in Alytes obstetricans—the midwife toad.
With them copulation normally takes place on dry land. The male extricates from the female the string of eggs, winds it round his hind legs and carries it about until the eggs are ready. Then, and not till then, he enters the water where the larvæ escape. If, however, one keeps these toads in a high temperature (25-30 C.) they enter the water to cool themselves and abandon their normal way of manipulating their brood because the string of spawn swells in water and does not remain sufficiently sticky to allow the male to fasten it to his thighs. The animals become gradually accustomed to live in water, and continue to carry on the business of reproduction there, even when the temperature is normal. As soon as the new instinct has become sufficiently established with the parents they beget offspring, which at a normal temperature go of their own accord into water to deposit their eggs, and also produce eggs more numerous than, and somewhat different from, those of the normal toad. Further, the males of this succeeding generation develop thumbs and forearms of a character which enables them to perform the difficult task of holding the females during copulation in the water.