1894.] YOUNG OF ECHIDNA ACULEATA. 13 



referred to here. But though Ornithorhynchus has probably 

 remained closer to the Prototherian stock than Echidna, the 

 presence of a horny bill in both forms as well as the characters to 

 which attention has recently been drawn by Westling 1 and Howes 2 

 seem to indicate the close genetic relation of the two genera, in 

 spite of their special adaptive characters. 



Note (Jan. 8th, 1894). — Since this paper was sent in for publi- 

 cation, I have received from Prof. Wilson and Mr. Martin a copy 

 of their recent paper, " Observations upon the Anatomy of the 

 Muzzle of Ornithorhynchus " (Macleay Memorial Volume, part 6), 

 in which it is stated that " the epidermis of the muzzle of Pla- 

 typus is no more ' horny ' than that of a dog's nose, from the 

 texture of which indeed it does not greatly differ." There is 

 no doubt, however, that in my specimens of the young of both 

 genera the horny layer of the epidermis covering the muzzle is 

 so thick as to justify one in speaking of a "horny" snout, even 

 though this is of course more flexible than the beak of a Turtle or 

 Bird : and in these specimens there can have been no possibility 

 of a partial desiccation. 



I should also mention that " the peculiar rod-like tactile organs 

 in the integument and mucous membrane of the muzzle of 

 Ornithorhynchus^ previously described by Poulton, have been 

 treated of by the same authors in part 7 of the ' Macleay Memorial 

 Volume,' in which it is stated that no such organs are present on 

 the anterior portion of the snout and palate of Echidna: this 

 agrees with my own observations. 



EXPLANATION OF THE PLATES. 



Plate I. 

 Fig. 1. Ventral view of a young Echidna aculeata, 125 cm. in length along the 

 dorsal curve (Stage I.). 



2. Ventral view of an older (male) specimen, 21 - 5 cm. in length (Stage II.). 



3. The snout in longitudinal section (Stage II.), the cut having been made 



to the left side of the septum nasi, so as to show the left nasal chamber. 

 The greater part of the glandular ridge on the septum has been re- 

 moved, the anterior part, enclosing Jacobson's organ, being left in situ. 



Plate II. 

 Figs. 4-11 represent transverse sections through the snout of Stage I. 

 Fig. 4. Through the external nostril and caruncle. 



5. Through the " ali-nasal turbinal," just in front of Jacobson's organ. 



6. Through the naso-palatine and Jacobson's ducts. 



7. Through about the middle of Jacobson's organ. 



8. Through the posterior end of Jacobson's organ. 



9. Rather farther back than fig. 8, showing the end of Jacobson's cartilage. 

 1U. Through the septal gland and maxillo-turbinal. 



11. Through the septal gland, maxillo-turbinal, and ethmo-turbinal. 



12. Section through the integument and a sweat-gland of the lower jaw 



(Stage II.). 



1 Bihang till K. Svenska Vet.-Akad. Handl. (Stockholm), Bd. xv. 1890. 



2 " On the Mammalian Pelvis, with special reference to the young of 

 Ornithorhynchus anatinus" Journ. Anat. and Physiol, vol. xxvii. (1893). 



