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Show 4 PROE. W. N. PARKER ON THE [Jan. 16, few remarks on the structure of certain parts of the head. The present paper refers to the same individuals, and treats of the external characters and the structure of the fore part of the head only; at a future time I hope to deal with other regions. The specimens are from the collection, of m y father, who received them from Dr. E. P. Ramsay, Curator of the Australian Museum, Sydney. I do not know of any description of the external characters of the young Echidna; and as such young specimens are very rarely obtained, I have thought it worth while to figure the two stages in m y possession (Plate I. figs. 1 & 2), the older of which is rather smaller thau the young Ornithorhynchus figured by m y father in his ' Mammalian Descent' (p. 25). I. Externcd Characters. Stage I. (Plate I. fig. 1).-The dorsal side is very convex, the head being bent so far round that the snout points directly backwards. The ventral side of the body is flattened, and the trunk passes insensibly into the conical tail, the apex of which is directed backwards. The length of the animal along the dorsal curve from the end of the snout to the tip of the tail is 12-5 cm., and the greatest diameter of the body 3 cm.; the head measures 2*8 cm. in length. The integument has a pitted appearance in the dorsal and lateral regions of the body, and though no hairs have yet appeared at the surface, the places in which the strong spines later break through can be plainly seen. The gape is narrow, and extends less than halfway along the snout, the anterior part of which is distinctly horny, the horn fading off posteriorly, so that the hinder part of the snout is covered with a soft integument like that of the rest of the head. The nostrils are ovoid and oblique, and a projecting septum extends into each from the inner side, about halfway across. Between the nostrils a distinct caruncle or " egg-breaker," like that of the young Ornithorhynchus', can be seen at this stage. Narrow slits indicate the position of the eyes, the upper and lower eyelids being confluent. The external auditory aperture is also slit-like, and extends into the thick layer of muscles covering the hinder part of the skull. The cloaca is shallow, and the vent is plugged by a rounded projection from its walls. The fore limbs are larger and stronger than the hind, and the digits are provided with well-developed claws, those of the 1st and 5th being smaller than, though forming a regular series with, the others. The hallux is short and small, and situated more proximally than the other digits of the pes: it has a well-marked claw. The hind toe is very large, its strong claw projecting far beyond those of the remaining three digits, which are of considerably less diameter than the 1st, and bear small claws. Stage II. (Plate I. fig. 2).-The flexure of the body is similar to that seen in Stage I., except that the end of the tail is n o w bent under the body, so that its conical end points towards the snout. 1 Cf. W. K Parker, 'Mammalian Descent' (London, 1885), pp. 45 & 49. |