DEVELOPMENT OF THE ALBINO RAT 253 
water. They are then stained in the Congo red solution, which 
may be diluted with distilled water about five times. With the 
diluted solution, the counterstaining requires one to two hours. 
The sections are then rinsed in distilled water, differentiated in 
80 per cent alcohol, dehydrated, cleared, and mounted in damar. 
Certain of the series were stained in Heidenhain’s iron-hema- 
toxylin and counterstained in Congo red. The drawings accom- 
panying this contribution were nearly all drawn on coarse ‘Ross 
board,’ with the aid of the camera lucida at a magnification of 
1000 diameters, using pencil and India ink. Such drawings 
admit of liberal reduction, and give a detail not readily obtained 
otherwise. Free use has been made of the Born method of re- 
construction, especially for earlier stages. The majority of 
the models thus obtained are here reproduced. 
I desire to express my sincere thanks and appreciation of the 
very material aid given me by Mr. Wayne J. Atwell, then Assist- 
ant in the Department of Histology and Embryology of the 
University of Michigan, in the making of the reconstructions 
of the oviducts included in this account. 
OVULATION, MATURATION, AND FERTILIZATION 
When this study was projected, it was the purpose to begin 
it with the stages of maturation and fertilization. During the 
time of material collection, there appeared the contribution of 
Sobotta and Burckhard: ‘‘Reifung und Befruchtung des Eies 
der Weissen Rate,’ covering these stages fairly completely. 
Duplication of their work did not seem necessary, so that my 
own studies begin with the pronuclear stage, to which stage the 
above mentioned investigators had carried their observations. 
Therefore, as concerns the process of ovulation, maturation, and 
fertilization as observed in the albino rat, I am confined for 
my data to the literature; from which a brief résumé is here 
made. 
The normal gestation period for non-lactating albino rats may 
be roughly estimated as from 21 to 23 days. As has been shown 
by King, the period of gestation of lactating albino rats varies 
