DEVELOPMENT OF THE ALBINO RAT 9 



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 resume 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 



