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alteration gradually disappeared when the inducing conditions were removed, except in a few instances in which it could not be demonstrated that the germ-plasm had not been directly affected.

Butterflies, moths, fishes, crustaceans, birds, guinea pigs, rabbits, trees, fungi, cereals, and bulbous plants have all been drawn into the experimental field with a remarkable unanimity of negation in so far as the somatogenic induction of characters was solely concerned, which might be fully transmissible to successive generations not under the influence of the exciting factors. Temperature, light, food, and composition of the medium or substratum all have been tested in their various effects. Only when the germ-plasm has been acted upon simultaneously with the soma has any well-defined reappearance of induced characters in succeeding generations been noted, and of the earlier results those of Standfuss and Fischer seem most notable, since in experiments with Vanessa and Arctia the application of special temperatures or the modification of nutritive conditions induced the formation of aberrant characters in some of the offspring. The new qualities were displayed in varying degree, and maintained their distinctive appearance in the products of hybridization with the parental strain. There seems to be some doubt among zoologists acquainted with these forms as to the significance of these results. It is not clear as

to the manner in which the formation of the new characters was induced. The experimental agencies employed affected both the soma and the germ-plasm segregated in the reproductive elements, and no interpretation of the facts would justify the conclusion that the aberrant qualities were somatogenically acquired.

While failure has attended all efforts to demonstrate the continued inheritance of impressions received by the body alone, a number of arrangements are found in nature which seem to demand such action for their explanation. Among these certain rudimentary organs, and also co-adaptations in which simultaneous specialization occurring in two or more members of the body has made for increased fitness, are difficult of interpretation without the interposition of somatic induction.

DIRECT STIMULATION OF THE GERM-PLASM IN BEETLES

Meanwhile the possibility of influencing heredity by agencies acting directly upon the germcells has awakened the keenest interest among biologists. The relations of soma and germplasm make it difficult to induce changes in the body without affecting the reproductive elements, while it is possible to devise experimental methods by which the egg or sperm alone may be subjected to modifying agencies. This has been done with such success that some very important

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FIG. 1. Leptinotarsa undecimlineata, normal form.

FIG. 2. Form derived from L. undecimlineata through the application of the climatic conditions. For convenience this form has been called angustovittata because it most closely resembles a species described by Jacoby, but it differs from angustovittata in many characters considered important by the systematists. [From Plate 16, Investigation of Evolution in Chrysomelid Beetles of the genus Leptinotarsa. Carnegie Institution, Publication No. 48, 1905. After Tower.]

FIGS. 3, 4. Normal mitosis of nuclei in cells of plant.

FIGS. 5, 6, 7, 8. Irregularities of mitosis in cells of onion roots resulting from exposure to radium. [After Gager.]

conclusions may be founded upon the evidence obtained. The results of the work by Tower, in which beetles of the genus Leptinotarsa were subjected to various combinations and alterations in climatic conditions in a series of experiments carried on for a period of more than twelve years, have recently been available and far surpass in importance anything previously obtained from animals. The value of the evidence is greatly enhanced by its repetition, by the fact that pedigreed cultures were used and conditions so regulated that an accurate analysis of the effects of the various climatic factors could be made.

Professor Tower finds that:

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Not only members of the genus Leptinotarsa, but also of allied genera can be directly modified by the application of intense environmental stimuli to the germinal material. The use of temperature and moisture in unusual degrees of intensity has given rise to a number of forms and modified characters. Some notion of the extent of these modifications is gained from the two following illustrations. In Plate I, Figure 1, is shown the normal form of L. undecimlineata, and in Figure 2, a race derived from it by the application of low temperature and low relative humidity. This new form resembles in some respects Jacoby's species L. angustovittata, and breeds true. It matters not whether this new form is a species, race, elementary species, or a nightmare to the systematist, the important point is, that as the result of subjecting the germinal material to certain conditions at a fixed point in its development, that the eggs thus treated, when fertilized by normal male germs, gave the form shown, which breeds true without subsequent segregation of charac

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