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Show 558 DR. R. VON L E N D E N F E L D O N T H E SYSTEMATIC [Dec. 21, other leg of the cock grew as usual. This experiment I have repeated several times in the same manner, with the same effects, which led me to conceive that the spur of a cock would not grow upon a hen, and that they were, therefore, to be considered as distinct animals, having very distinct powers. In order to ascertain this, 1 took the spurs of hen chickens and placed them on the legs of young cocks. I found that those which took root grew nearly as fast, and to as large a size as the natural spur on the other leg, which appeared to be a contradiction to m y other experiments. Upon another examination of m y hens, however, I found that the spurs had grown considerably, although they had taken several years to do it ; for I found that the same quantity of growth in the spur of a cock, while on the cock, during one year, was as much as that of the cock s spur on the hen in the course of three or four years, or as three or four to one ; whereas the growth of the hen's spur on the cock was to that of the proper spur of tbe hen as two to one." When a female animal belonging to a dimorphic species assumes male characters, it is truly an example of Atavism, or development of transmitted characters normally latent. This part of the matter has been dwelt upon at some length for the following important reason. If we regard the epiblast and the structures developed therefrom as representing the chief characters derived from the male parent, it opens up a field of interesting inquiry in clinical medicine and pathology regarding hereditary diseases, and it demonstrates clearly enough that we have little knowledge concerning the germs of organs which may be latent in an animal; therefore Neogenetic Atavism is, at its best, exceedingly questionable. To assume that such a form of Atavism exists, is to believe in the sudden development of new characters : this is totally opposed to the fundamental principles of Evolution. The question is one of great importance to the pathologist, inasmuch as there is very great probability that many aberrations of organs and tissues are atavistic in their nature. 2. O n the Systematic Position and Classification of Sponges. B y R. v. L E N D E N F E L D , Ph.D., F.L.S., Assistant in the Biological Laboratory of University College, London. [Received December 20, 1886.] I. Introductory Remarks, p. 558. IT. Nomenclature of Spicules, p. 559. III. The Systematic Position of Sponges, p. 564. IV. The Classification of Sponges, p. 570. V. Key to the Recent Families of Sponges, p. 589. VI. Appendix. List of Publications, p. 592. I. INTRODUCTORY REMARKS. Our knowledge of the development and structure of Sponges is of such recent date that we have hardly had time to utilize it for systematic purposes till now. |