UEPKODUCTIVE CYCLE IN DASYUBUS YIVEBRINUS. 149 
occurred free in the pouch alongside an attached one. In the 
other, ten young were found, six attached, three free in tlie 
pouch, and oue outside considerably shrivelled. 
Gestation Period. 
Attention has already been called to the fact that ovulation 
is entirely independent of copulation, a fact which renders it 
extremely difficult, it' not impossible, to determine accurately 
the length of tlie gestation period. One of us has already 
recorded that ‘Hhe shortest period observed between coitus 
and the birth of the young was a little over eight days,” 
hence it was concluded that the time of gestation does not 
exceed this period” (14). Selenka, it may be noted, gives 
the gestation period of Didelphys as barely eight days (23). 
As regards our eight-day record, we think it is desirable to 
give further details. Copulation was observed on June 
7th, about ten a.m. It lasted a comparatively short time. 
The female was killed on June 15th at six p.m. A single 
young one (recently born, and measuring 7*5 mm. greatest 
length in the fresh state) was found in the pouch, which was 
greatly enlarged and possessed prominent sebaceous glands. 
Our notebook record continues, assuming that copulation 
had not taken place before receipt of this female, we can put 
down the gestation period as a little over eight days.” There 
are two points in this record which should be noted : first, the 
brevity of the copulation, and second, the question of copula- 
tion previous to receipt. The recollection of one of us 
regarding this particular female is that she was brought in by 
the collector, placed at once with the male, a short copula- 
tion, or an attempt at the same, ensuing almost immediately. 
In view of the impossibility of entirely excluding the 
occurrence of copulation previously, we cannot regard the 
foregoing evidence as absolutely conclusive as to the length of 
the gestation period. At the same time it should not be 
forgotten that a female once served will not under normal 
circumstances again copulate. It is of course quite possible 
