194 
CHAS. H. O’DONOGHUE. 
knob-area. In the second the club-shaped anlage grows 
markedly inwards, and thus increases greatly in length (see 
Text-fig. 1, e), and finally a hollow appears within it, trans- 
forming it into a deep cavity, the teat-pocket (see Text- 
fig. l,p). It is to the second type that Dasy u rus viverrinus 
belongs. From this stage onwards we find that all marsu- 
pials follow a similar course of development. 
The deep aspect of the club-shaped anlage is formed by a 
layer of columnar cells, which have remained passive during 
the preceding changes. Now, however, they give rise to solid 
bud-like outgrowths — the “ primary outgrowths” — which 
grow outwards from the deeper parts of the anlage into the 
surrounding tissue (see Text-fig. 1, D and r). From these 
original outgrowths arise similar solid projections — the 
t( secondary outgrowths.” The primary outgrowths become 
transformed into hair-follicles, which produce strong hairs, 
and which also give rise to their appropriate sebaceous 
glands, these latter arising from the follicles as tertiary out- 
growths. The secondary outgrowths, the anlagen of the 
mammary glands, grow into the surrounding tissue as solid 
cellular cords, which, however, become hollow and slightly 
branched at their distal ends. 
In the pouch young of D. viverrinus three months after 
birth, I find that the marsupium is already laid down as a 
small, shallow, circular depression, in which are situated the 
teat anlagen. The anlagen, which in the specimen under 
consideration (No. 1) were six in number — three on each side 
of the middle line — Fave the form of hollow invaginations of 
the epidermis. This latter is considerably thickened in these 
teat areas, so that it forms a many-layered stratified epi- 
thelium. Each of the teat anlage is provided with six very 
strong hairs, whose follicles run down from the base of the 
epidermal invagination into the underlying tissue. These 
follicles constitute the primary outgrowths of Bresslau (see 
above). From the upper part of each primary outgrowth 
there arises a cellular cord, the secondary outgrowth. This 
is solid proximally, but in its deeper part it becomes hollow, 
