Darwin himself had concluded, from his own experience and that of others, that injuries and similar inflicted acts of violence are the cause of hereditary consequences only in cases where they bring about some long-continued and wasting disease, and thus produce some permanent effect on the bodily constitution. For this reason, especially injuries to main nerve-tracts in parts near the centres are readily accompanied by hereditary consequences, because they interfere with the nutrition of the members supplied by them. Brown-Séquard has observed in a great number of cases of guinea pigs whose nerve-roots he had severed, that the offspring of the animals operated upon developed diseases of the eyes, ears, and other organs which conformed regularly to the character of the operation, and could therefore be predicted; and also noted malformations and deficiencies, amounting even to the complete disappearance of the eye-balls, such as never arise or have been observed in these animals without violent interference. His positive results regarding the hereditability of the evil consequences of disturbing operations have a decided advantage in numbers and scope over the negative results of Weismann; and it is not clear how the belief in the non-hereditability of somatic conditions will accommodate itself to them. But if conditions of the body produced by such sudden interferences have under certain circumstances entailed hereditary consequences, how much more should we expect this same result from slowly effected constitutional changes, which external influences, working uninterruptedly for hundreds of years, bring about in an organism which has been transported into a new element, into new surroundings, or into a different climate. Not at all infrequently does the coming together and union of two new organisms beget hereditary changes which can be explained only through the direct influence of the one upon the other. Thus, for example, in the case of plants in hot countries which are protected against the assaults of leaf-devouring ants by body-guards of smaller ants, and also in species of quite different families, as, for example, in _Cecropia_ of the order _Euphorbiaceæ_, and in some _Triplaris_ species among the _Polygonaceæ_, we find little chambers, approachable through small openings in the stems, which serve the ants protecting the plants as dwelling and breeding places. Are we to believe now, in regard to this fact, that these plants, so different in their nature, have produced through voluntary variations the stems which contain these openings, or are we to believe we have to deal here with openings acquired through inheritance which originally were bored in the stems by the ants at the most appropriate points? Surely the first conclusion, which would uphold Weismann’s theory, has but a very slight degree of probability in its favor, whilst the latter, which would overthrow his view, is very highly probable. And such examples could be