AND MAMMARY FCETUS OF THE ECHIDNA HTSTEIX. 
685 
of chelonians and birds, by which they break their way through the harder calcareous 
covering of their externally hatched embryo. 
Some modification of epiderm has been removed from the tubercle in the young 
Echidna (Plate XLI. fig. 11, e\ as in the young Ornithorhynchus* '. 
Description of the Plates. 
PLATE XXXIX. 
Female Echidna {Echidna Ilystrix, Cuv.), two-thirds nat. size. 
a. Left " Marsupial " or " Mammary " pouch, with young as seen therein. 
b. Right ditto empty. 
<?. Tail-stump of Echidna. 
d. Outlet of cloacal vestibule. 
e. Young or " mammary foetus," as removed from the pouch; two-thirds nat. size. 
PLATE XL. 
Fig. 1. Section of abdominal integument, with mammary glands of the Echidna exposed 
from the inner side. 
a. Left mammary gland ; cL Right mammary gland. 
b. Ducts converging to fundus of mammary pouch. 
d. d l . Part of " panniculus carnosus " acting as compressor of the gland. 
e. Fascia forming a capsule of the gland, reflected. 
f. Skin of abdomen. 
Fig. 2. Section of abdominal integument, and left mammary gland and pouch. 
Fig. 3. Section of abdominal integument, and right mammary gland and pouch. 
c. Cavity of pouch ; the other letters as in figure 1. 
Fig. 4. Orifice of mammary pouch, expanded to expose the mammary areola. 
Fig. 5. Mammary areola magnified to show the orifices of the lacteal ducts, and p, seba- 
ceous papillae. 
Fig. 6. Young or "mammary foetus" of Echidna Hystrix: nat. size: side view. 
Fig. 7. Ditto : front view. 
Fig. 8. Ditto : back view. 
Fig. 9. Ditto : under view. 
Fig. 10. Ditto: upper view. 
Figs. 11 & 12. Ditto: fore-foot magnified. 
Figs. 13 & 14. Ditto: hind-foot magnified. 
* Transactions of the Zoological Society, vol. i. pi. sxsiii. fig. 8. 
