C7G FROFESSOH OWEN ON THE MABSUHAX POUCHES, .MAMMARY (iLANDH, 
is associated with so great a development of the inverted tegumental*}' fold, as to make 
the mammary relation seem a very subordinate and reduced one. Hut in the Marsu- 
pial series there is a gradation:; and both in Thi/lari mis and in the small dorsigerous 
Opossums of South America (l)i<h'l]>Itj/s dorsir/rra, /). mvriva, /A jMsilla, &c), the mar- 
supial structure, if shown at all. is represented by a pair of shallow semilunar fe.ssa\ 
with their concave outlets opposite to each other, as in Echidna. 
In tiiis comparison the distinctive peculiarity of the parts in the terrestrial Mono- 
treme is tin? absence of a teat, or of any rudiment of such : no part of the fundus of the 
pouch is again everted, produced, or folded about tin* terminal ducts of the mammary 
gland, so as to form a pedicle by which the young could take hold with the mouth, and 
so suspend itself and suck. 
The question remains, whether the marsupial pouches of the Eckid/nct increase with 
the growth of the young 1 ? It is certain that they commence with the growth or 
enlargement of the mammary glands preliminary to birth. 
In that young specimen of female EckidfWt in which the glands were first discovered*, 
their ducts opened upon a plane surface of the abdominal integument. In a nearly 
full-grown unimpregnated 6 male, preserved in spirits, which I examined and com- 
pared with the breeding mother here described, there is also a total absence of inflected 
folds of the integument where the mammary duels terminate. 
Some movement, perhaps, of these ducts iu connexion with the enlargement of the 
mammary lobes, under the stimulus of preparation for a coming offspring, may, "with 
associated growth of the abdominal integument surrounding the areola, be amongst 
the physical causes of the first formation of the pouch. 
It lias already been remarked that the integument of the pouch, especially as it 
approaches the fundus, is thinner than that, covering the abdominal surface of the 
body, from whieh (he pouch is Continued. Such tegumental^ growth, continued with 
the pressure of the pari of the growing young within, may lead to a marked increase 
of size ; to be reduced, perhaps, by absorption and shrinking of tin* skin concomitantly 
with red net ion of t he mammary glands after tin* term of lactation has expired. I much 
doubt, however, whether the increase of size of the pouch would ever be such as to 
include and wholly conceal the young animal ; it more probably, at the later period of 
lactation} serves only tO admit the head or beak. Thus the ordinary condition of sucking 
would be reversed iu these Australian Mammals; instead of the excretory ducts on 
an everted process of integument being taken into the mouth, this is received into an 
inverted pouch into which the milk is poured* 
I have not hitherto met with any trace or beginning of such abdominal pouches in 
the various OPTtithorhynchi in which I have had occasion to note different phases of the 
development ol the ovaria and mammary glands')'. 
• PhiloHnphi. ul Tr;:n«actions, I K'iL\ p. 5U7, PI. XVII. fign. 2 A :i. 
t **0a thi liammary Glands of the DrniOtorhynekx^ ^wwAmv/ji," Philosophical TruiiNuctions, L882, p. .">17. 
1*1. XV. Will. 
