170 
J. P. HILL AND OHAS. H. o’dONOGHUE. 
ditioiis^^ (Heape, loc. cit., p. 18). We propose here to 
consider this question very briefly in the light of such evidence 
as we have of the oestral cycle in the Marsupials and Mono- 
tremes, which in respect of their reproductive phenomena 
generally (but making exception of the pouch of the Mar- 
supials) are undoubtedly more primitive than the Eutheria. 
We have already shown earlier in this paper that the cestrous 
cycle in Dasyurus occurs only once in the breeding season, 
i. e. that Dasyurus is monoestrous. As regards other 
Marsupials we have no definite evidence, but our records, and 
those of others (Semon ( 25 ) Caldwell ( 5 )), indicate that 
Trichosurus, Phascolarctus and Phascolomys breed but 
once a year, each species having its own particular breeding 
time, regularly recurring. We think in view of the posi- 
tive evidence we have concerning Dasyurus, the cautious 
statement of Heape (loc. cit., p. 21) that among certain 
wild animals which are known to undergo parturition only 
during a very circumscribed time, the monoestrous condition 
may be assumed as probable may be accepted 
and applied to the forms mentioned. 
Selenka, however, makes the definite statement in regard 
to Didelphys marsupialis ( 23 , p. 104) — ^^Die Brunst der 
Weibchen tritt normaler Weise nur ein Mai im Jahre ein. 
Wenn aber den Mutterthieren die Jungen kurz nach dem 
Gebaren aus dem Beutel fortgenommen warden oder wenn die 
Begattung, was ofter vorkam, aus Mangel an Geschicklichkeit 
der Mannchen nicht gelang, so konnen die Weibchen 4-6 
Wochen spater zum zweiten male im Jahre briinstig werden, 
spatestens jedoch Anfang Juni.’’ 
Further, with reference toHypsiprymn u s cuniculus, he 
states ( 24 , p. 174) — Die herrannahende Brunst . . . zu 
verschiedenen Jahreszeiten, im Friililing, Herbst und Winter 
beobachtet wurde.” 
Wiltshire, again ( 27 , p. 397), states on the authority of 
Bartlett that the kangaroos in the Gardens of the Zoological 
Society "Misplay sexual excitement in September . . . 
and also in our spring month of April.^’ 
