We are now come to the preliminaries of copulation. We have described them in our work, making use of the observations of Balbiani, Gruber, and of Engelmann, some of which we found confirmed by Bütschli. M. Maupas, who has recently again taken up this question, believes he has discovered in his predecessors, or rather in the observations of M. Balbiani, grave errors. I shall transcribe the passage in question: "When a numerous group of Infusoria of the same species are found in the conditions that determine copulation, these animalcula abandon themselves to certain movements, and exhibit an agitation the significance of which has been much exaggerated. Balbiani, who in fact always seeks analogies with the higher animals, has given us an animated description of these movements, to which a poetical imagination has contributed at least as much as exact and scientific observation. This description has met with a most favorable reception among certain philosophers and psychologists who have taken up with it in the belief that they could thereby reveal in microzoans the rudiments of the instincts and psychic faculties of higher-organized beings. As there is very much inexactitude and exaggeration in all that, it is time to calm this enthusiasm and to refer the facts and their explanation to some more exact criterion." (Page 413.) I believe it useless to occupy my time in dealing with the aggressive tone that this author has seen fit to assume towards me, and which seems to be habitual with him when he criticises the works of people with whom he does not agree. I shall carefully examine his observations and seek to derive from them some profit, to the improvement and correction of my work upon the Psychic Life of Micro-Organisms, if it is true that I have committed the grave errors of which he speaks. Besides, the question of the preliminaries of copulation is so interesting in itself that I have no fear of turning to it a second time.