The absence of any good evidence of this direct kind in favour of use-inheritance will be rendered strikingly apparent to any one who reads a learned and interesting work by Professor Semper[62]. His object was to show the large part which he believed to have been played by external conditions of life in directly modifying organic types--or, in other words, of proving that side of Lamarckianism which refers to the immediate action of the environment, whether with or without the co-operation of use-inheritance and natural selection. Although Semper gathered together a great array of facts, the more carefully one reads his book the more apparent does it become that no single one of the facts is in itself conclusive evidence of the transmission to progeny of characters which are acquired through use-inheritance or through direct action of the environment. Every one of the facts is susceptible of explanation on the hypothesis that the principle of natural selection has been the only principle concerned. This, however, it must be observed, is by no means equivalent to proving that characters thus acquired are not transmitted. As already pointed out, it is impracticable with species in a state of nature to dissociate the distinctively Darwinian from the possibly Lamarckian factors; so that even if the latter are largely operative, we can only hope for direct evidence of the fact from direct experiments on varieties in a state of domestication. To this branch of our subject, therefore, we will now proceed. [62] _Animal Life_, International Scientific Series, vol. xxxi. CHAPTER IV. CHARACTERS AS HEREDITARY AND ACQUIRED (_continued_). (C.) _Experimental Evidence in favour of the Inheritance of Acquired Characters._ Notwithstanding the fact already noticed, that no experiments have hitherto been published with reference to the question of the transmission of acquired characters[63], there are several researches which, with other objects in view, have incidentally yielded seemingly good evidence of such transmission. The best-known of these researches--and therefore the one with which I shall begin--is that of Brown-Séquard touching the effects of certain injuries of the nervous system in guinea-pigs. [63] The experiments of Galton and Weismann upon this subject are nugatory, as will be shown later on. But since the above was written an important research has been published by Mr. Cunningham, of the Marine Biological Association. For a full account I must refer the reader to his forthcoming paper in the _Philosophical Transactions_. The following is his own statement of the principal results:--