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Show 576 MR. M. E. WOODWARD ON [N.&\ 5 On making an examination of the clarified jaws (Plate XXVI fig. 29) of a young animal (hairless), one is immediately struck with the correctness of the greater part of these figures, but in respect to the first premolar they appear to be incorrect, for no trace is observable of Bate's dpm. 1. In order to be certain that I was not dealing with an abnormal specimen, I examined the clarified jaws of three specimens of about the same age as that studied by Bate, two others being cut one into horizontal and the remaining into frontal sections ; three younger animals were also examined by the section method1. In all 10 half heads were investigated, and as these obtained from various localities, all agreed amongst themselves in respect to the relations of the 1st premolar, I cannot but come to the conclusion that Bate's observations on this point are erroneous and that the teeth which he describes as ,pm" have no existence. In the younger specimen all the deciduous teeth save the 1st premolar were well calcified, but the germs of the permanent teeth though distinct were but little differentiated. An examination of a horizontal section at this period (figs. 27 and 28) shows pm. 1 developing in a position precisely similar to that occupied by the reduced deciduous incisor, canines, and premolars; and, as is the case with the latter, the former exhibits a specialized portion of the dental lamina on its lingual surface, the only observable difference being that dpm. 1 is larger, uncalcified, and generally more backward than the other milk-teeth ; also that the germ of ppm. 1 is slighter but might well be thought capable of developing at a later period. That this is not the case is seen from an examination of the older stage: here all the deciduous teeth are strongly developed and even dpm. 1 is now calcified (fig. 31); it is, however, very large snd not at all of the nature of a vestigial needle-shaped tooth such as figured by Bate, but rather presents all the characteristics of the tooth regarded by him as ppm. 1. The permanent incisor, canines, and premolars (fig. 30) are now highly differentiated, with large enamel and dentine germs : a comparison of one of these with the indication of the germ of ppm. 1 (Plate X X V I . fig. 31, dl.), shows that the latter is now less marked than in the earlier stage and is obviously aborting; consequently Me may safely assert that it never attains any degree of specialization, but remains merely a slight swelling of the dental lamina. The entire absence of any labial development from that portion of the dental lamina between the large enamel-organ of this tooth (dpm. 1) and the epithelium of the mouth, taken together with the position occupied by it, viz. one similar to that of the true milk-teeth, and the specialized thickening of the dental lamina on its lingual side, exactly resembling in appearance and position the true 1 In all 3 stages were examined, including two specimens of stage 1, one the 2nd, and five of the 3rd stage, all being older than Leche's stages. (1) 55 m m . total length ; 17 m m . head length. (2) 58 „ ,. „ 18 „ „ (3) 95 „ „ ,, 30 „ ,, ,, |