As an example of looseness of expression I may quote the following from Weismann: “A useless or almost useless rudimentary part may often be injured or torn off _without causing processes of selection to occur which would produce in it a capacity for regeneration_. The tail of a lizard again, which is very liable to injury, becomes regenerated because, as we have seen, it is of great importance to the individual and if lost its owner is placed at a disadvantage.” And as an example of vagueness, the following statement commends itself: “Finally the complexity of the individual parts constitutes the third factor which is concerned in regulating the regenerative power of the part in question; for the more complex the structure is, the longer and the more energetically the process of selection must act in order to provide the mechanism of regeneration, which consists in the equipment of a large number of different kinds of cells with the supplementary determinants which are accurately graduated and regulated as regards their power of multiplication.” Without attempting to disentangle the ideas that are involved in these sentences, let us rather attempt to get a general conception of Weismann’s views. In a later paper (1900), in reply to certain criticisms, he has stated his position somewhat more lucidly. In the following statement I have tried to give the essential part of his hypotheses: Weismann believes the process of regeneration to be regulated by “natural selection”; in fact, he states that it has arisen through such a process in the lower animals--since they are more subject to injury--and that it has been lost in the higher forms except where, on account of injury, it has been retained in certain parts. Thus when Weismann speaks of regeneration as being an adaptation of the organism to its environment, we must understand him to mean that this adaptation is the result of the action of natural selection. We should be on our guard not to be misled by the statement that because regeneration is useful to the animal, it has been acquired by natural selection, since it is possible that regeneration might be more or less useful without in any way involving the idea that natural selection is the originator of this or of any other adaptation. It will be seen, therefore, that in order to meet Weismann on his own ground it will be necessary to have a clear understanding in regard to the relation of regeneration to Darwin’s principle of natural selection. With Weismann’s special hypothesis of the “mechanism,” so-called, by which regeneration is made possible we have here nothing to do, but may consider it on its own merits in another chapter.