192 
CHAS. H. O’DONOGHUE. 
drawn at the same magnification by means of a camera lucida 
with a^ i n - oil-immersion objective and a N o. 2 Zeiss ocular. 
The photo-micrographs also, with the exception of the first, 
are all taken at a uniform magnification of 16 diameters, 
and the reproductions are from the untouched negatives. I 
have to express my thanks to Mr. F. Pittock, of the Zoological 
Department of this College, for his valuable assistance in the 
preparation of these photographs. For convenience of 
description, the material investigated is arranged under six 
headings: (1) Formation of the gland; (2) the adult gland ; 
(3) changes prior to ovulation ; (4) changes during preg- 
nancy; (5) changes after parturition ; and (6) changes when 
ovulation is not succeeded by pregnancy. 
Formation of the Gland. 
Bresslau (8) has shown that the earliest recognisable stage 
in the development of the mammary organs of the marsupials 
appears in the form of small lenticular thickenings of the 
Malpighian layer of the epidermis (see Text-fig. 1, a). Each 
of these lenticular structures foreshadows one of the teats with 
its corresponding glands in the adult, and consequently it 
may be distinguished as the teat anlage. This latter then 
proliferates, and assumes a club-shaped form (see Text-fig. 1, b), 
while the cutis around it thickens and forms areolar tissue. 
The club-shaped condition is maintained for some time, 
during which the pouch-formation commences. 1 Thus far 
the development of the teat anlage follows a similar course in 
all the marsupials, but from this stage onwards Bresslau 
recognises two different types. In the first, the club-shaped 
structure alters in form and again becomes more flattened, 
and while it is still small a crescentic space appears within it 
(see Text-fig. lc). The thickened epidermal walls of this 
space are entirely constituted by the cells of the original 
1 It is not the purpose of the present note to deal with the growth 
and homologies of the pouch, a subject which has been fully treated in 
a recent paper by Bresslau (9). 
