I think that it will be in agreement with the doctrines of general pathology to assume that such a development involves two dangers; first, that of _inhibition_, and secondly, that of _regression_. That is to say, owing to the general tendency to variation in biological processes it must necessarily happen that not all these preparatory phases will be passed through and completely outgrown with the same degree of success; some parts of the function will be permanently arrested at these early stages, with the result that with the general development there goes a certain amount of inhibited development. Let us seek analogies to these processes in other fields. When a whole people leaves its dwellings in order to seek a new country, as often happened in earlier periods of human history, their entire number certainly did not reach the new destination. Apart from losses due to other causes, it must invariably have happened that small groups or bands of the migrating people halted on the way, and settled down in these stopping-places, while the main body went further. Or, to take a nearer comparison, you know that in the higher mammals the seminal glands, which are originally located deep in the abdominal cavity, begin a movement at a certain period of intra-uterine development which brings them almost under the skin of the pelvic extremity. In a number of males it is found that one of this pair of organs has remained in the pelvic cavity, or else that it has taken up a permanent position in the inguinal canal which both of them had to pass through on the journey, or at least that this canal has not closed as it normally should after the passage of the seminal glands through it. When as a young student I was doing my first piece of scientific research under v. Brücke, I was working on the origin of the dorsal nerve-roots in the spinal cord of a small fish, still very archaic in form. I found that the nerve-fibres of these roots grew out of large cells in the posterior horn of the grey matter, a condition which is no longer found in other vertebrates. But soon after I discovered that similar nerve-cells were to be found outside the grey matter along the whole length to the so-called spinal ganglion of the posterior roots, from which I concluded that the cells of this ganglion had moved out of the spinal cord along the nerve-roots. Evolutionary development shows this too; in this little fish, however, the whole route of this passage was marked by cells arrested on the way. Closer consideration will soon show you the weak points of these comparisons. Therefore let me simply say that we consider it possible that single portions of every separate sexual impulse may remain in an early stage of development, although at the same time other portions of it may have reached their final goal. You will see from this that we conceive each such impulse as a current continuously flowing from the beginning of life, and that we have divided its flow to some extent