AM) .MA.MMAKY FOETUS OP THE ECOffEDNi EYSTfiDt G75 
tion of the animal at Melhourne. The lobules of each gland convene toward the mesial 
lino, in their course to terminate in the fundus of the pouch. Each lobe is a solid 
parenchymatous body; the duct is more directly continued from a eaual uhieh maybe 
traced about halfway toward the fundus of the lobule; the eaual gives off numerous 
short branches from its circumference, which subdivide and terminate in clusters of suh- 
spherieal " acini M or secerning cellules. The structure is oil the sime general plan as 
that of the mammary glands in higher mammals, but, the cellules are proportionally 
larger; it closely resembles the structure of the lobes of the same glands in the Orni- 
thorhynehus, and in neither Monotreme can the elongated lobes be properly termed 
M |»yriform c;ccal pouches." 
The converging termination of the lacteal ducts at the fundus of a pouch, or inverted 
fold of the skin, resembles the disposition of those parts in the (efacrtr; save that here 
tin* ducts terminate on a prominence or nipple projecting from the fundus of the pouch 
into its cavity ; whilst, in the Echidna they terminate in the smooth and even concave 
surface of the fundus of the pouch. 
Calling to mind Mr. Morgans observation of the concealed nipple in an inverted sac 
of the tegument at the fundus of the pouch in the young or non-breeding Kangaroo, 
where, instead of a, nipple, then* was seen only c 5a minute circular aperture, resembling 
in appearance the mouth of a follicle" *, J made sections of both the marsupial or 
mammary pouches and glands (Plate XI,. figs. 2 & :>) satisfactorily demonstrating thai no 
inverted or concealed nipple or any rudiment or beginning of such existed ; and. indeed, 
had any such arrangement like that of the Kangaroo been characteristic of the mam- 
mary organization of the Echidna, the glands being functionally active and well deve- 
loped in the female dissected, such nipple would have been everted, and would have 
served, as the first observer of the young animal in the pouch believed, to have attached 
and suspended it to the parent. 
But it is evident that the young simply nestles itself within the marsupial fossa, 
clinging, it may be, by its precocious claws to the skin or hairs of that part, and im- 
bibing by its broad, slit-shaped mouth tin* nutritious secretion as it is pressed by the 
mUSCleS acting upon the gland from the areolar outlets of the ducts. 
The skin of the abdomen, where it begins to be inverted, loses thickness, and at the 
fundus of the pouch (ib. fig. 1, Z>, fig. 3, c) is only half as thick as where it overspreads 
the abdomen (ib. fig. 1,/). This modification, and the relation of the pouches to (he 
mammary glands, prove the structures shown in Plate XXXIX. a, 5, and Plate XL. 
tigs. 2 & :;, r, to be natural, not accidental. 
The pair of lateral folds or clefts into the bottom of which the lacteal duds open, in 
the Echidna are homologous with those similarly related to the mammar\ glands in 
Cetaceans, and also to the more developed folds or pouches in Marsupials. In Ceta- 
ceans the pair of tegumentary clefts have exclusive functional relations to the mam- 
mary organ; in Marsupials the superadded office of receiving and protecting the young 
* m A Description of the Mammary Organs of the Kangaroo/* Linn. Trans., vol. xvi. p. 62, pi. tig. 1 . A. 
