DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 579 
It would appear probable that we must be prepared to en- 
tertain favorably Klaatsch’s suggestion that the “ Placentals ” 
have originally all passed through a kind of marsupial stage, 
“ein Form, die jederseitz zwar eine Mammartasche, aber 
keinen Beutel besass.” He denominates the animals which 
exhibited this form “ Taschentiere ” or “ Bursalia.” 
Such a rudimentary or primitive condition must have been 
a characteristic of the common stock of both Meta- and 
Eutheria, and was only a marsupial one in the sense in 
which Echidna is now marsupial. 
Klaatsch has recently pointed out (83) what strong reason 
there is for the surmise that the evolution of mammary pouches, 
such as Echidna possesses, is probably an even older trait of 
mammalian development than the evolution of the mammary 
glands themselves. Its existence in the oviparous Echidna 
proves that it isa much older mammalian characteristic than any 
form of placental connection can possibly be. We cannot follow 
Hubrecht (35) in his assumption that the Protamniote an- 
cestors of the Promammalia (and of the Sauropsida) must 
have been viviparous. 
In our view the Monotremes must be taken to represent a 
quite distinct offshoot of a common Promammalian (Hypo- 
therian) stem, which was originally both oviparous and “bursal”’ 
(in the sense of Klaatsch), and in which both hairs and mam- 
mary glands were gradually developed. We do not believe that 
in the long run it will be found possible to maintain the essential 
dissimilarity of the mammary glandular organ in Monotremes 
(36, and cf. Minot, 1. c., pp. 565-6). 
After the separation of the Monotreme phylum we must 
suppose the placenta to have appeared, constituting the steck 
protoplacental. At all events, the existence of a placenta in 
the marsupial order seems to indicate that the primitive pouched 
common ancestors (Bursalia) of the Meta- and Eutheria, 
long after losing their oviparous character, developed an 
allantoic placental connection between the embryo and the 
uterine wall. At the same time the mammary function, 
already evoked during the oviparous period for the nourish- 
VOL. 39, PART 4,—NEW SER. RR 
