AND MAMMARY FCETUS OR THE ECHIDNA HYSTRIX. 
675 
tion of the animal at Melbourne. The lobules of each gland converge toward the mesial 
line, 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 canal which may be 
traced about halfway toward the fundus of the lobule; the canal gives otf numerous 
short branches from its circumference, which subdivide and terminate in clusters of sub- 
spherical “ acini ” or secerning cellules. The structure is on the same 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 hi the Orni- 
thorhynchus, and in neither Monotreme can the elongated lobes be properly termed 
“pyriform cgecal 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 Cetacea ; save that here 
the 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 Mi'. Morgan’s 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, there was seen only “ a minute circular aperture, resembling 
in appearance the mouth of a follicle” *, I made sections of both the marsupial or 
mammary pouches and glands (Plate XL. figs. 2 & 3) satisfactorily demonstrating that 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 the 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, b, fig. 3, c) is only half as thick as where it overspreads 
the abdomen (ib. fig. 1 ,f). This modification, and the relation of the pouches to the 
mammary glands, prove the structures shown in Plate XXXIX. a, b , and Plate XL. 
figs. 2 & 3, c, to be natural, not accidental. 
The pair of lateral folds or clefts into the bottom of which the lacteal ducts open, in 
the Echidna are homologous with those similarly related to the mammary 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 
* “ A Description of the Mammary Organs of the Kangaroo,” Linn. Trans., vol. xvi. p. 62, pi. 2. fig. 1, 5. 
