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Show 1894.] YOUNG OE ECHIDNA ACULEATA. 7 The question as to the presence of rudiments of true teeth in Echidna is of especial interest. After a fruitless search through sections of the older stage, I hoped to be more successful in the younger specimen, but have not succeeded in finding any indication of the development of teeth at all, and am confident that earlier stages must be examined before any signs of these organs can be recognized. It is certainly remarkable for all traces of them to have disappeared so early, especially when we consider how well they are developed in Ornithorhynchus': this is probably to be accounted for by the extreme and early specialization of the mouth iu Echidna. The fact that Rose" has succeeded in finding traces of teeth in a small embryo of Manis 7*6 cm. long, while they have entirely disappeared in older embyros from 17-30 cm. in length, further indicates the probable formation and early reduction of a " Zahn-leiste " in Echidna. IV. The Nose and Jcccobson's Organ. In the note already referred to I drew attention to the marked development of Jacobson's organ in Echidna, and to the fact that it possesses a " turbinal" supported by cartilage. The organ had been previously recognized in Ornithorhynchus by Sir W . Turner 3 and m y father4, and sections of a young specimen of this animal in m y possession showed that it closely resembles that of Echidna. Since the publication of m y note, however, Dr. Symington" has given such an excellent account of the nose of Ornithorhynchus, comparing it with that of other Mammals and also giving the literature of the subject, that it will be only recessary for m e to refer to this animal for purposes of comparison with Echidna. In each stage I bisected the head to one side of the septum nasi. The half in which the latter was intact was then decalcified and cut into serial sections, the other half being used for purposes of dissection. Fig. 3 (Plate I.) represents a longitudinal section of the head at the older of the two stages, and shows the form and relations of the nasal cavity, which is 2*5 cm. in length. A comparison with a figure of the adult given by Zuckerkandl6 shows that the natal cavity is now comparatively short and broad (compare also transverse sections of both stages, figs. 5-11, 14, and 15, Plates II. & III.). The cartilaginous nasal capsule is more complicated than in 1 Cf. E. B. Poulton, Quart. Journ. Micros. Science, vol. xxix. 1888; and Old-field Thomas, Proc. Roy. Soc. vol. xlvi. 2 C. Rose, Anat. Anz. vii. Jahrgang, 1892, p. 618. 3 " The dumb-bell shaped bone in the palate of the Ornithorhynchus compared with the pre-nasal bone in the Pig," Journ. Anat. and Physiol, vol. xxv. 4 ' Mammalian Descent,' London, 1885, pp. 52 and 54. 5 " On the Nose, the Organ of Jacobson, and the Dumb-bell-shaped Bone in the Ornithorhynchus," Proc. Zool. Soc. 1891, p. 575. 6 E. Zuckerkandl, ' Das periphere Geruchsorgan der Saugethiere,' Stuttgart, 1887, pi- i- ng. 3. |