1912] Long: Living Eggs of Rats and Mice 121 
in turn supports above a second tube or sleeve (d. sl.), to which 
the dise (disc) is attached. This arrangement allows free rota- 
tion of the disc and prevents any torsion in the spring being 
communicated to the sleeves. But for this, the dise might turn 
back and break the capillary tube which passes from the slide 
into the bottle. A collar (cl.) with set-serew determines the 
greatest height at which the disc is supported by the spring. In 
preparation for changing the fluid in the slide it is only necessary 
to depress the dise, rotate it until the desired bottle is in place, 
and then allow the spring to raise it so that the capillary tube 
passes into the bottle. 
When one fiuid is to be used for some time, evaporation from 
the bottle is greatly reduced by having the upper end of the neck 
ground perfectly flat and covering it with a piece of a polished 
glass slide (cover, fig. K). This cover is perforated by a hole 
just large enough to admit freely the capillary tube. As the 
slide on the stage of the microscope is moved about by the 
mechanical stage the cover slips over the polished surface of the 
neck. 
OBSERVATIONS 
Eggs for study were in all cases obtained from the oviducts. 
Knowing that in mice ovulation occurs fourteen or more hours 
after parturition, it is only necessary to know when a litter is 
born and to kill the female fourteen to seventeen hours later. Out 
of fifteen mice killed for live eggs, seven, killed on the average 
16.2 hours, and two, killed 24 and 25 hours, respectively, after 
parturition, contained eggs in the oviducts. In two other cases 
the exact time was not known. In the four cases in which eggs 
were not found the average time was 19.9 hours. In successful 
cases the eggs were easily visible in a fold of the oviduct near 
the ovary. Previous work on fixed material demonstrated that 
soon after ovulation the eggs are in the above fold of the oviduct, 
where they he in a cluster surrounded by corona or follicle cells, 
and that later, as they pass along the oviduct, they become 
separated and lose the enveloping follicle cells. Study of live 
material abundantly substantiates the earlier findings, for the 
cluster of eggs and follicle cells can be identified through the 
