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Show 6 PROF. W. N. PARKER ON THE [Jan. 16, An examination of the end of the snout with a hand-lens shows the presence of a number of fine dots on both jaws extending about as far back as the gape. These are indicated in figs. 1 and 2. Sections show them to be due to the presence of funnel-shaped apertures in the horny layer, which extend inwards, surrounded by a continuation of the horn, and gradually become narrower (figs. 4, 5,12, and 13). Just beneath each aperture the epidermis is prolonged inwards to form an elongated oval process (fig. 12), which, slightly below the base of the dermal papillae, narrows somewhat to form a tube extending for some distance into the derma, where it becomes convoluted ; its walls are composed of a double layer of cells, and the lumen becomes greatly coiled on passing into the swollen base of the epidermal process and then communicates with the aperture at the base of the horny ingrowth. It will thus be seen that these glands are precisely similar in structure to ordinary sweat-glands. I should mention that the lumen is not developed in the young stages. Poultona has described structures in Ornithorhynchus which are apparently similar to these, and suggests that they may correspond to modified hairs ; this, however, seems tome improbable. 1 have found nothing which could correspond to the sensory organs of the bill of Ornithorhynchus described by Poulton. N o hairs, nor any structures resembling hairs, are present on the horny snout. Behind this, hairs are developed in abundance (figs. 2 and 10), and in the older stage the sebaceous glands can be seen arising as buds from the hair-follicles. No sweat-glands are present on the hairy part of the head; the rest of the body I have not yet examined. It should, however, be remembered that Gegenbaur 2 has shown that the mammary glands are modified sweat-glands in these animals. III. The Oral Cavity. Even in the younger stage the mouth has already acquired its narrow and tubular form (see figs. 5-7, 10, and 14). The elongated tongue is covered with a thin layer of horn at the tip. The sublingual glands are numerous, and open at various points into the floor of the mouth. The naso-palatine canals communicate with the oral cavity anteriorly (fig. 6, np.c.) ; and from this point backwards, some distance beyond Jacobson's organ, a number of simple gland-tubes, very similar to those already described in the snout, are present on the roof of the mouth (fig. 7). Similar glands are also present in this region in the young Ornithorhynchus. The epithelium in certain regions both above aud below gives rise to horny teeth, which on the anterior part of the lower jaw form marked ridges (figs. 5, 7,14, 16). A dermal papilla extends into the thickened epithelial ridge, which produces a thick horny layer on its outer surface. 1 " O n the tactile terminal Organs and other Structures in the Bill of Ornithorhynchus" Journ. Physiol, vol. v. p. xv. (Proc. Physiol. Soc. 1884). 2 ' Zur Kenntniss der Mammarorgane der Monotremen,' Lfipzisr. ISSfi |