138 
,]. r. HILL AND (JHAS. H. o’dONOGHUE. 
in two pouch-young Bresslau records the presence of four pairs, 
whilst in a third he found three primordia on one side, four 
on the other. In the pouch-young, the mammary primordia 
are arranged symmetrically in two slightly curved longitu- 
dinal rows, the two primordia of the posterior pair lying 
nearest the middle line, those of the anterior pair most remote 
from it, so that the two rows already show the same horse- 
shoe shaped arrangement as is characteristic ot‘ the adult. 
Round each mammary primordium, which has meantime 
grown into the cutis as a kuob-shaped epidermal projection, 
a ring-shaped epidermal thickening arises and this later 
liollows out to form a circular groove — the marsupial pocket — 
bounded by a circular wall. The lateral portions of the walls 
of the three pockets on each side then join so as to form a 
continuous lateral pouch fold and finally the two folds become 
continuous with each other in front and behind, and so pro- 
duce the circular wall of the pouch. The occurrence of 
supernumerary nipples (Hypermasty, Hyperthely) in D. 
viverrinns is of interest in view of the fact that D. hallu- 
catus, according to Oldfield Thomas (28) normally possesses 
eight teats, that species of Phascologale and Sminthopsis 
(which genera are regarded by various authorities as being 
more primitive than Dasyurus), have ten, whilst higher 
numbers still are met with amongst the Didelphzidte (Peramys- 
heuseli, 17-25). These facts, as Bresslau (4, p. 805-8) has 
pointed out, would appear to indicate that Dasyurus, like many 
other marsupials, has suffered, in the course of phylogeny, a 
reduction in the number of teats within the pouch, which reduc- 
tion has affected those more anteriorly situated. In the case 
of the pouch with only five teats, it seems as if six mammary 
rudiments were included in the pouch, but for some reason or 
other the anterior one on the right side failed to develop. 
Wlien the young are born, they are transferred to the 
pouch, presumably by the mother with the aid of her lips, 
and, as they become permanently fixed to the teats for some 
time, the number of teats determines the maximum number 
of young that can be reared in one litter. 
