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Show 224 DR. R. UR00M ON THE ORGAN OF [Mar. 18, (3) The granules are especially well-developed upon the first and second caudal segments and upon the last abdominal tergite, against all of which the point of the sting can be forcibly scraped. On the third caudal segment, upon which the sting is capable of but little movement, they are scarcely or not at all developed, and upon the fourth and fifth, which cannot be touched by the point of the sting, they are absent. (4) The longitudinal flatness of the granular area on the first ami second caudal segments, which results from the uprising of the groove and the elevation of the anterior part of the upper surface, can be explained on the supposition that it is designed to give the sting a long and continuous sweep from segment to segment, without the danger of catching against their posterior edges or of wounding the artbrodial membrane. It is difficult to see what other interpretation is to be put upon this special and unique modification of the segments in question. 3. On the Organ of Jacobson in the Elephant-Shrew (Macroscelides proboscideus). By R. BfiOOM, M.D., B.Sc.1 [Received February 4, 1902.] (Plate XXI.2) From the examination of the organ3 of Jacobs-on in a large series of mammals, I, in 1897, concluded that it varies surprisingly little in even very dissimilar genera of a common Order. In the Marsupialia the chief Polyprotodont genera have their organ of Jacobson very much alike, while even in the Diprotodonts the organs are all formed on a type which differs but little from that found in the Polyprotodonts. While in all the Rodents, so far as examined, the organ is formed on a single peculiar type which seems to be a modification of that found in the Marsupials, in the higher mammals a single type of organ is found in forms so varied iis the Hedgehog, Bat, Lemur, Cat, Sheep, and Pig. It would thus appear that the organ of Jacobson is but little influenced by the habits of the animal, that it remains a clear indicator of the early family relationships of a genus when almost all the other ancestral characters have been so modified as to be scarcely recognizable, and that hence it is of considerable importance in determining the precise affinities of aberrant mammals. Having recently had occasion to make a series of sections of the snout of a foetal Elephant-Shrew (Macroscelides proboscideus), in connection with a study of the development of the palatine process of the premaxilla, 1 Mas naturally much interested in observing the condition of Jacobson's organ, especially as W . K. 1 Communicated by Prof. G. B. HOWES, F.R.S. - For explanation of llie Plate, see p. 227. s Trans. R. Soc. Edinb. vol. xxxix. p. 2'3-L. |