Guthrie exchanged the ovaries of black and white fowls, and concluded that a change was brought about in them, but Daven port's later experiments have shown that no such effects are pro duced. Guthrie's results were probably due either to impurity in the birds or to regeneration of the original ovary. Castle and Phillips transplanted the ovaries of a black guinea-pig into a white. When mated to a white male black offspring resulted.
It has been shown by a number of experimenters that the colours of moths and butterflies are affected by extremes of tem perature, and there are a few records, particularly those of Stand f uss, showing that some of the extreme aberrations may be inherited. But there is no evidence to prove that the induced effects are transmitted from the body to the germ-cells.
Pictet has reported that when caterpillars are fed on leaves other than their natural food, the colour of the moth may be changed. When two or three generations have been so reared, and the next generation is returned to normal food, some of the effects may still persist. It seems not unreasonable to conclude from the rather meagre evidence that the results are due to the weakened condition of the germ-cells, or other general metabolic effects. Pictet has also reported that when caterpillars are forced to feed on foreign plants their progeny may then select the same foreign food rather than that usual for the race. The evidence does not suffice to establish the conclusion that the change is due to inheritance of an acquired habit, but if the results are confirmed they open up other interesting possibilities.
W. Heslop Harrison has described the appearance of melanic forms in the moth Selenia after feeding on leaves treated with lead nitrate or manganese sulphate. The evidence points to the con clusion that the treatment brought about the change and that the change was directly on the germ-cells. The melanic types that appeared—one a dominant, the others recessive—were shown to give Mendelian inheritance when crossed to the type-forms.
Beginning in 1907 P. Kammerer has brought forward case after case supporting, he believed, the doctrine of the inheritance of acquired characters. He studied the effect of coloured surround ings on the skin-colour of the spotted salamander (S. maculosa).
Placed on a yellow background the young salamander develops, as it reaches the adult stage, more yellow, while on a black back ground, it develops more black. Offspring from the former de velop on a yellow background even more yellow than their parents and on a dark background more yellow than does the ordinary salamander when so treated. Similarly the offspring of artificially produced black salamanders become blacker than did their parents on a black background.
These experiments when repeated by others (Secerov, Herbst, von Frisch, Przibram-Dembowski, Boulenger) have shown that the background does affect the relative amount of yellow or of black on an individual, but it has never been shown that the effects are transmitted. It is also realized that there are many possible sources of error of interpretation (purity of material, unconscious selection of the most responsive parents and personal judgment based on selected individuals). Experiments of this sort are, as we now realize, open to several possible errors unless these are carefully guarded against, which has not been done in the majority of reported cases. The same adverse criticism applies to Kammerer's other experiments ; for example, to those with the secondary sexual character (thumb-pads) of the midwife-toad (Alytes) ; with the effect of heat on the eggs of lizards; with the transplanted ovaries of dark and light races of salamanders ; and with the length of siphons of the ascidian Ciona. In every one of these cases the facts he reports have been either contested or dis proved. The lack of quantitative data in Kammerer's work and his too ready acceptance of unsubstantiated evidence of others, has aroused wide scepticism. His appeal to popular audiences for unprejudiced judgment of his results in his book on the Inher itance of Acquired Characters is not likely to win the case, and the recklessness with which he has made positive statements about other biological topics creates an unfavourable impression of his ability to reach an unbiased conclusion on a question that calls for high critical judgment.