All are agreed that natural selection alone is insufficient to explain all, if any, of the processes of degeneration. All either consciously or not admit the principle of panmixia, and all are now agreed that this process alone can not produce extensive degeneration. All are agreed that the important point is degeneration beyond the point reached by panmixia, the establishment of the degenerating process, whatever it may be, in the germ, or, in other words, the breaking of the power of heredity. It is in the explanation of the latter that important differences of opinion exist. Weismann attempts to explain the degeneration beyond the point which panmixia can reach by a process which not only is insufficient, even if all his premises are granted, to produce the desired result without the help of use transmission, but has as its result a horizontal degeneration which has no existence in fact. Romanes supposed degeneration, beyond the point which may be reached by panmixia, to be the result of personal selection and the failure of the hereditary force. The former is not applicable to the species in question, and is denied by such an ardent Darwinist as Weismann to be applicable at all in accounting for degeneration. Moreover, the process as explained by Romanes would result in a horizontal degeneration which has no existence in fact. The second assumption, the failure of hereditary force, is not distinguishable, as Morgan has pointed out, from the effect of use transmission. [Illustration: FIGS. 1-6.--Photographs of the upper halves of the heads of specimens of nearly the same length under the same magnification, to show the gradual decrease of the eye. The dotted line leads to the eye in all cases. FIG. 1.--_Zygonectes notatus._ FIG. 2.--_Chologaster papilliferus._ FIG. 3.--_Chologaster Agassizii._ FIG. 4.--_Amblyopsis spelæus._ FIG. 5.--_Troglichthys rosæ._ FIG. 6.--_Typhlichthys subterraneus._ ] The struggle of parts in the organism has not affected the eye through the lack of room, since the space formerly occupied by the eye is now filled by fat and not by an actively functioning organ. It is not affected by the struggle for food, for stored food occupies the former eye space. It could only be affected by the more active selection of specific parts of food by some actively functioning organ. It is possible that this has in fact affected the degeneration of the eye. The theory explains degeneration in the individual, and implies that the effect in the individual should be transmitted to the next generation. This second part seems but the explanation of the workings of the Lamarckian factor.