bo 
Or 
DEVELOPMENT OF THE OPOSSUM 
e. Are the eggs of operated animals normal? 
The question may well be asked whether we are dealing with 
normal material in the case of eggs removed some time after an 
abdominal operation under anesthesia or whether such treat- 
ment of the mother affects the development of the eggs un- 
favorably. It should be emphasized at the outset, however, 
that whatever answer we give to the question does not affect the 
conclusions reached in this study, which is supported by an 
abundance of material from freshly killed animals and by a 
large assortment of specimens removed from animals at the first 
operation. It should also be noted that the time interval 
between the two operations was in many cases only a few hours 
or a half-day, so that in this material, too, the chances of modi- 
fying the normal course of development of the eggs were reduced 
to aminimum. From a careful examination of my notes and a 
scrutiny of both classes of material I have concluded that there 
is no evidence pointing to deleterious effects of the operation, 
and I here present some of the facts that have led me to this 
conclusion. 
In the first place, the condition of the operated animals was 
as good or better than that of non-operated cage animals; for 
the former were the choice specimens, vigorous in health and 
sexually active. As stated above, I am now able to determine, 
with a high degree of accuracy, the near approach of oestrus in 
the female opossum. A surprisingly large number of females 
are captured (and by the terms of our contract with the hunters 
must be purchased) which are either too old or too sick to breed. 
Specimens with deep, infected wounds, intestinal diseases, 
xerophthalmia (McCollum), or other nutritional disturbances do 
not come into heat. Only once or twice have I seen females 
with badly infected wounds continue in the oestrus cycle like a 
normal animal; but I have records of dozens of cases in which 
the normal sexual processes were interrupted by wounds or dis- 
-ease during pro-oestrus or dioestrus. Pregnant females, how- 
ever, pass successfully through the period of gestation even in 
