1894.] TOUlSrG OF ECHIDNA aculeata. 5 



My two specimens of this stage measure respectively along the dorsal 

 curve from the end of the snout to the tip of the tail 21*5 cm. (see 

 fig. 2) and 25*5 cm., the greatest diameter of the body being about 

 6 cm., and the head 4 cm. in length. The rough integument is 

 covered with papillae, and the stiff bristles now project about 3 mm. ; 

 the position of the stronger and sparser spines amongst these can 

 be seen more plainly than in the earlier stage, though they still 

 hardly project above the surface. The snout is more plainly 

 marked off from the rest of the head than in Stage I., and is relatively 

 flatter : it is entirely covered with horn, and much resembles the 

 " beak " of Omithorhynchus except in the relative extent of the gape. 

 The nostrils are now more completely valvular, and the caruncle 

 is no longer recognizable. The eyelids are beginning to separate, 

 the conjunctival chamber communicating with the exterior by a 

 small aperture. The cloaca has become deeper, folds of the integu- 

 ment radiating out from the vent. 



The integument on the ventral side of the body is much folded ; 

 and in the larger of the two specimens, which is probably a female, 

 a shallow triangular pouch, the apex of which points backwards, 

 can be seen between and rather anteriorly to the hind limbs. 

 There can be little doubt that this represents the mammary pouch 

 as described by Haacke * ; and as it is so distinct at this stage, it 

 seems improbable that it would altogether disappear in the adult 

 between the periods of suckling. I do not propose to treat of its 

 structure or of its relation to the pouch of Marsupials in the present 

 paper 2 . 



The pes is now nearly as large as the manus, though its claws 

 are not so strongly developed. The calcaneal spur can be seen in 

 both specimens, but is considerably larger in the smaller of the 

 two, which is probably a male. 



II. Integument of the Head. 



The resemblance of the snout to that of Omithorhynchus has 

 already been remarked upon ; and this is more particularly the case 

 in the later stage, in which it is relatively flatter than in the 

 younger one. As in Omithorhynchus, the lips, as well as the whole 

 integument of the snout, are immobile, owing to the development of 

 a thick horny layer from the epidermis (Plates II. & III.). The horn 

 is much thicker in the older of the two stages, and this is all the 

 more remarkable as in the adult the skin in this region can hardly 

 be said to be horny at all. The horny layer extends over the 

 margins of the gape, and then thins off gradually : it also passes 

 inwards to line the external narial passages (Plate II. fig. 4 and 

 Plate III. fig. 13). The caruncle (figs, land 4) is formed by a ridge 

 of the epidermis on which the horn is especially thick 3 . 



1 W. Haacke, " On the Marsupial Ovum, the Mammary Pouch, and the Male 

 Milk-glands of Echidna hystrix," Proc. Roy. Soc. vol. xxxviii. p. T2 ; and Biol. 

 Centralblatt, viii. 



2 Cf. H. Klaatsch, Morph. Jahrbuch, Bd. xvii. p. 483. 



3 Cf. Carl Rose, " Ueb. die Zahnleiste und die Eischwiele der Sauropsiden," 

 Anat. Anz. vii. Jahrgang, 1892, p. 748. 



