1894.] young or 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 tbe 

 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 

 in Echidna. 



The fact that Eose 2 has succeeded in finding traces of teeth in a 

 small embryo of Manis 7*6 cm. long, while they have entirely 

 disappeared in older embjros from 17-30 cm. in length, further 

 indicates the probable formation and early reduction of a " Zahn- 

 leiste " in Echidna. 



IV. The Nose and Jacobson'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 my father 4 , and sections of a young specimen of this animal 

 in my possession showed that it closely resembles that of Echidna. 

 Since the publication of my 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 necessary for me 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. 



Tig. 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 Zuckerkandl ° shows that the nasal 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 Of. E. B. Poulton, Quart. Journ. Micros. Science, vol. xxix. 1888 ; and Old- 

 fielrl Thomas, Proc. Roy. Soc. vol. xlvi. 



2 C. Rose, Anat. Anz. vii. Jahrgang, 1892, p. 618. 



:| " The dumb-bell shaped bone in the palate of the Ornithorhynchus com- 

 pared with the p re-nasal bone in the Pig," Journ. Anat. and Physiol, vol. xxv. 



4 'Mammalian Descent,' Loudon, 1885, pp. 52 and 54. 



s " On the Nose, the Organ of Jacobson, and the Dumb-bell-shaped Bone in 

 the Ornithorhynchus," Proc. Zool. Soc. 1891, p. 575. 



8 E. Zuckerkandl, ' Das periphere Geruchsorgan der Saugetbiere,' Stuttgart, 

 1887, pi. i. fig. 3. 



