Let us now take a brief survey of a class of facts in the case of which we may most abundantly observe the power of memory in organised matter. We have ample evidence of the fact that characteristics of an organism may descend to offspring which the organism did not inherit, but which it acquired owing to the special circumstances under which it lived; and that, in consequence, every organism imparts to the germ that issues from it a small heritage of acquisitions which it has added during its own lifetime to the gross inheritance of its race. When we reflect that we are dealing with the heredity of acquired qualities which came to development in the most diverse parts of the parent organism, it must seem in a high degree mysterious how those parts can have any kind of influence upon a germ which develops itself in an entirely different place. Many mystical theories have been propounded for the elucidation of this question, but the following reflections may serve to bring the cause nearer to the comprehension of the physiologist. The nerve substance, in spite of its thousandfold subdivision as cells and fibres, forms, nevertheless, a united whole, which is present directly in all organs—nay, as more recent histology conjectures, in each cell of the more important organs—or is at least in ready communication with them by means of the living, irritable, and therefore highly conductive substance of other cells. Through the connection thus established all organs find themselves in such a condition of more or less mutual interdependence upon one another, that events which happen to one are repeated in others, and a notification, however slight, of a vibration set up {77} in one quarter is at once conveyed even to the farthest parts of the body. With this easy and rapid intercourse between all parts is associated the more difficult communication that goes on by way of the circulation of sap or blood. We see, further, that the process of the development of all germs that are marked out for independent existence causes a powerful reaction, even from the very beginning of that existence, on both the conscious and unconscious life of the whole organism. We may see this from the fact that the organ of reproduction stands in closer and more important relation to the remaining parts, and especially to the nervous system, than do the other organs; and, inversely, that both the perceived and unperceived events affecting the whole organism find a more marked response in the reproductive system than elsewhere. We can now see with sufficient plainness in what the material connection is established between the acquired peculiarities of an organism, and the proclivity on the part of the germ in virtue of which it develops the special characteristics of its parent.