The Mechanism of Evolution in Leptinotarsa

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1918 Excerpt: ...first group of species, showing that the principles at work are the same. The fertility between these two groups of three species is very low, and thus far the only series of crosses that has been at all successful are the two lines from the crossing of decemlineata and diversa, described in the early portion of this chapter, and which gave such unusual results. Only two have given adult progeny out of many trials. No other successful crossing between the two groups has been attained. This has been attempted, but there seems an aversion of the two series to one another, so that copulation can not be obtained excepting at the climax of reproductive activity, and then is best attained if the antennae are cut off or covered with neutral gum, so that the sex-reactions depending upon the odors of the species secretions comes feebly or not at all into play. By subterfuges of one sort or another I have been able to make all the possible combinations of these two groups of species, able to obtain matings and fertilized eggs in all of them, most of which developed for short periods, but few of which hatched. Very many die before or at the period of the forming of the limbbuds. The two groups have quite different rates of development, Ac values, and differences in these may be primarily responsible for the death of the embryos. It may be possible to produce hybrids between these groups by the altering of the Ac values through the use of external conditions, but thus far the permanent alteration of this character has not been affected by this agency. It is shown in this and the preceding chapters that this character or the agents which it represents are specific for the species, and, while capable of change, has in all thus far tested shown rigid upper and lower limit...