In the results of these experiments, as described, there is one feature which I regard as quite unaccountable. Tower makes no comment upon it. Indeed, from the general tenour of the paper, I infer, not only that he does not perceive that he is recounting anything contrary to usual experience, but rather that he regards the result as conforming to expectations previously formed. The point in question is the genetic behaviour of the dominant normals produced under the abnormal conditions. These normals were the result of the breeding of parents declared to be at the same time giving off many recessive gametes. Some of these normals must be expected therefore to be heterozygous unless some selective fertilisation occurs. Nevertheless in every case they and their offspring are reported to have continually bred true. I allude especially to the tables given on pp. 288, 289, 292, and 293. Tower does not mention any misgiving about this result, and I think he regards himself as recounting phenomena in general harmony with the ideas of mutation expressed by De Vries. This they may be; but to anyone familiar with analytical breeding the course of these experiments must seem so surprising as to call for most careful, independent confirmation. In 1910[10] Tower published an account of further experiments with _Leptinotarsa_. The work described related to two subjects. Crosses were made between three forms, _undecimlineata_ Stål, _signaticollis_ Stål and "_diversa_" named by Tower as a new species. The distinctions between these three depend partly on characters of the adults and partly on those of the larvae. The adults of _undecimlineata_ and _diversa_ have the elytra striped, but the elytra of _signaticollis_ are unstriped. The larvae of _signaticollis_ and of _diversa_ are yellow, but those of _undecimlineata_ are white.[11] Moreover, in _signaticollis_ and _diversa_ the black increases in the third stage of the larvae to form transverse bands which are absent in _undecimlineata_. The general course of the experiments shows that these differences may be approximately represented as due to the action of three factors, any of which may be independently present or absent. The stripings of the elytra and of the larvae are each due to a separate factor. As regards the distinction between the yellow and the white larvae the evidence does not prove that there is decided dominance of either colour and I infer that the heterozygotes are often intermediate. The chief contribution which this new paper claims to make relates to differences in the results which ensue from crosses effected between these three types at different average temperatures. We are first concerned with four experiments which I number (1), (2), (3), (4):