The headquarters of the genus is evidently as Tower states, in Mexico and the adjoining countries. In this region there is a great profusion of forms, some very local, some as for instance the well-known _decemlineata_,[8] more widely spread. The distinctions are almost all found in peculiarities of colour and pattern, and the limits of species are even more indefinable than is usual in multiform animals. Tower arranges the various types into seven groups of which the one most studied is that which he calls the _lineata_ group. To this group belong all the forms to which reference is here made, and, as I understand, they differ among themselves entirely in size, colour and pattern. There is no suggestion of infertility in the crosses made between the several forms of the _lineata_ group; in fact they present, like many Chrysomelidae, a good example of what most of us would now call a polymorphic species, consisting of many types, some found existing in the same locality, others being geographically isolated. A series of experiments was devoted to the attempt to fix strains corresponding to the extremes of continuous variations. For example, those with most black pigment and those with least black taken from a population continuously varying in this respect, were separately bred; but almost always the selection led to no sensible change in the position of the mean of the population. The variations in these cases were evidently fluctuational. In some instances, however, real genetic differences were met with, and strains exhibiting them were, as usual, rapidly fixed. Tower points out that several of the varieties (or species, as he prefers to call them) were obviously recessive to _decemlineata_. This is most clearly demonstrated in the case of the form called _pallida_, which is a pale depauperated-looking creature, with the orange of the thorax almost white and the eyes devoid of pigment.[9] This form behaved as an ordinary Mendelian recessive, breeding true whenever it appeared in the cultures, or when individuals found wild were studied in captivity. A black form which Tower names _melanicum_ was similarly shown to be a Mendelian recessive. Wild specimens of this variety of opposite sexes were not found simultaneously in nature, and there was thus no opportunity of breeding them together, but the hereditary behaviour was seen in the F_{2} generation from a _melanicum_ found coupled with _decemlineata_. Experiments also occurred giving indication that a variety with the stripes anastomosing in pairs (_tortuosa_), was another recessive, and that a variety--called "_rubri-vittata_"--gave an intermediate F_{1} with subsequent segregation. All these are forms of _decemlineata_ Stål.