Ze, CARL G. HARTMAN 
The drawings on plate 12 were made free hand by Mr. T. H. 
Bleakney from stained specimens in oil of wintergreen, the 
size being calculated from photographs of the living eggs. The 
eggs shown in text figure 4 were mostly drawn from wax models 
made after the Born method, x 600. This figure was also 
drawn on Ross board No. 2, but was reproduced one-third of 
the original size. All other drawings, except a few where 
especially mentioned, were made from sections and were drawn 
as nearly like the specimens as possible, imperfections and all. 
The attempt was made to reproduce not only the form, but 
also the texture of the specimens, and for this purpose the Ross 
board has proved to be a delicate and responsive medium. 
The smaller drawings were outlined with the camera lucida at 
a magnification of x 300, x 1200, x 3000 (reduced to x 50, 
x 200, x 500); the larger sections of blastocysts, since they had 
to be drawn at a magnification of 1200 which resulted in draw- 
ings more than a meter long, were first sketched x 400 with 
a Leitz-Edinger drawing apparatus, then photographed and the 
negative finally projected to the desired magnification by the 
Edinger apparatus. To facilitate measurements, the scale of a 
stage micrometer was drawn beside the first sketch made and 
appears upon the negative made from it. 
The photomicrographs were made with Spencer lenses, which 
afford a flatter field for photographing than the Zeiss microscope. 
lenses. Attention is especially directed to the photographs of 
living eggs. More than 500 different eggs are represented in 
the heliotypes. All of the photographs on plates 1, 2, and 11 
and many other figures are magnified eight times and some are 
at a higher magnification. 
The photographs are unretouched and are reproduced as 
exactly like the original as was possible with the process 
employed. 
To secure an absolutely black background for the photographs 
taken by reflected light, we found it best to use a black watch- 
glass. The eggs are removed from the uterus and placed in a 
deep watch crystal in clear Ringer’s solution free from dirt and 
blood-cells. The watch erystal is now set into the watch-glass 
