48 MAMMALIAN DESCENT. [LECT. II. 



HUXLEY, Prof., " On the Application of the Laws of Evolution to the 

 Arrangement of the Vertebrata, and more especially of the 

 Mammalia," Proc. Zool. Soc., Dec. 14, 1880, pp. 649-662. 



LUTKEN, Dr CH. W., "A Letter to the Secretary of the Zoological 

 Society," Proc. Zool. Soc., March 4, 1884, pp. 150-152. 



MURIE, Dr JAMES, F.Z.S., &c., "Remarks on the Skull of the 

 Echidna from Queensland," Proc. Linn. Soc., vol. xiv., 

 Zoology 1879, pp. 413-417. See also Captain Armit's 

 " Notes," supra. 



OWEN, Prof. RICHARD, F.R.S., I. "On the Marsupial Pouches, Mammary 

 Glands, and Mammary Foetus of the Echidna hystrix," Philo- 

 sophical Transactions, 1865, plates xxxix.-xli., pp. 671-686. 

 II. " On the Ova of Echidna hystrix" Philosophical Transac- 

 tions, 1880, plate xxxix., pp. 1051-1054. 



PARKER, W. K., F.R.S., " On the Shoulder-girdle and Sternum," Ray 

 Society's Publications, 1868, plate xviii., pp. 192-194. 



At present, data are wanting to enable us to form a thoroughly 

 clear idea of what a primary mammal, an original, ancient " Proto- 

 there," must have been like. For, at present, we are only very partially 

 masters of what Nature has left for us to work out, namely, the 

 structure and development of the two types that still linger on the 

 planet. One tiling we do see, however, and that is, that those two 

 forms are far more unlike in their adult than in their embryonic (or 

 early) condition (see Owen, I., plate xl., figs. 6-10). The beak, when 

 undeveloped, does not differ in essentials in the two genera, namely, 

 Omithorhynchus and Echidna (Tachyglossus and Acanthoglossus). 



In the figure of the young Ornithorhynchus given by Professor 

 Owen, and in that made for me from a young specimen nearly as 

 large as a man's fist (p. 25, fig. 2), two very important characters can 

 be seen in the beak. 



1. The first of these is that the fore part of the bill or beak 

 arises out of a swollen basal or hind part, which ensheaths the 

 proximal part of the free beak, exactly as in the non-flying birds 

 (Ostrich, Emeu, Cassowary), and their nearest relatives, the Tinamous 

 of South America. See Dr P. L. Sclater, M.A., F.R.S., "On 

 Struthious Birds," Trans. Zool. Soc., vol. iv., plates lxvii a .-lxxvii., 

 pp. 353-364. 



