4 PROF. w. N. PAEKJiH, ON 'rHB [Jan. 16, 



few remarks on the structure of certain parts of the head. The 

 present paper refers to the same indiAdduals, and treats of the 

 external characters and the structure of the fore part of the head 

 only ; at a future time I hope to deal with other regions. 



The specimens are from the collection of ray father, who received 

 them from Dr. E. P. Eamsay, Curator of the Australian Museum, 

 Sydney. I do not know of any description of the external cha- 

 racters of the young Echidna ; and as such young specimens are 

 very rarely obtained, I have thought it worth while to figure the 

 two stages in my possession (Plate I. figs. 1 & 2), the older of which 

 is rather smaller than the young Ornitliorhynchus figured by my 

 father in his ' Mammalian Descent' (p. 25). 



I. External Characters. 



Stage I. (Plate I. fig. 1). — The dorsal side is very convex, the 

 head being bent so far round that the snout points directly back- 

 wards. The ventral side of the body is flattened, and the trunk 

 passes insensibly into the conical tail, the apex of which is directed 

 backwards. The length of the animal along the dorsal curve from 

 the end of the snout to the tip of the tail is 12-5 cm., and the 

 greatest diameter of the body 3 cm. ; the head measures 2-8 cm. in 

 length. The integument has a pitted appearance in the dorsal and 

 lateral regions of the body, and though no hairs have yet appeared 

 at the surface, the places in which the strong spines later break 

 through can be plainly seen. The gape is narrow, and extends less 

 than halfway along the snout, the anterior part of which is dis- 

 tinctly horny, the horn fading off posteriorly, so that the hinder part 

 of the snout is covered with a soft integument like that of the rest 

 of the head. The nostrils are ovoid and oblique, and a projecting 

 septum extends into each from the inner side, about halfway 

 across. Between the nostrils a distinct caruncle or " egg-breaker," 

 like that of the young Ornithorhym-hus^, can be seen at this stage. 

 Narrow slits indicate the position of the eyes, the upper and 

 lower eyelids being confluent. The external auditory aperture is 

 also slit-like, and extends into the thick layer of muscles covering 

 the hinder part of the skull. The cloaca is shallow, and the vent 

 is plugged by a rounded projection from its M'alls. 



The fore limbs are larger and stronger than the hind, and the 

 digits are provided with well-developed claws, those of the 1st 

 and 5th being smaller than, though forming a regular series \vith, 

 the others. The hallux is short and small, and situated more 

 proximally than the other digits of the pes : it has a. well-marked 

 claw. The hind toe is very large, its strong claw projecting far 

 beyond those of the remaining three digits, which are of considerably 

 less diameter than the 1st, and bear small claws. 



Stage II. (Plate I. fig. 2). — The flexure of the body is similar 

 to that seen in Stage I., except that the end of the tail is now bent 

 under the body, so that its conical end points towards the snout. 



' Cf. W. K. Parker, 'Mammalian Descent' (London, 1885), pp. 45 & 49. 



