1912] Long: Living Eggs of Rats and Mice 111 
For studying and experimenting on living eggs of mammals, 
apparently no suitable apparatus has ever been made. Several 
conditions must be fulfilled by a successful apparatus: the 
temperature of the microscope and accessory apparatus must be 
fairly constant; there must be some way of keeping the eggs that 
are under observation in suitable artificial media, of seminating 
them, and of removing the excess spermatozoa. To meet these 
requirements the writer has devised and constructed the two 
pieces of apparatus now to be described. They consist of a 
double-walled box, made of glass and wood, heated to a constant 
temperature by an automatically controlled electric current, and 
of a circulation slide, in which eggs can be placed for study and 
experimental treatment. 
CONSTANT-TEMPERATURE Box FOR MICROSCOPE 
The box (figs. D to H, and pls. 16 and 17), which is large 
enough to contain two microscopes, a compound and a binocular, 
and also accessory apparatus and cultures, measures inside at 
the level of its floor about 30 by 18 inches, (76 by 45.5 em.). The 
greatest side height is about 1114 inches (29em.). The box 
is supported on legs. The general appearance and shape is so well 
shown in the photographs (pls. 16 and 17) and in the vertical 
sectional view (fig. D) that only a brief explanation is necessary. 
As can be seen in figure D, the upper part of the box, which 
is the part containing the microscopes, ete., is so shaped that 
the operator can work near the microscope with the least incon- 
venience, and so that the least light is cut off from the mirror, 
whether by reflection from the glass of the sloping front or by 
the lowness of the roof. 
The walls of the upper part are of heavy glass (about 14 inch, 
or 5 mm. thick) except the back and ends (pl. 16 and fig. D) 
which are of wood, and are double except at back, where there 
are holes through which the hands are passed in working. The 
end walls are covered inside with glass plates (fig. E and pl. 17), 
so that the box is lined with glass save for the back and floor. 
Where glass plate comes into contact with glass plate one or 
both edges are ground perfectly straight to ensure a tight joint. 
Details of the construction can be seen in figures D and E. The 
