DEVELOPMENT OF THE ALBINO RAT iy, 
here and there to the inner surface of the parietal ectoderm, in 
the albino rat at no time forming a continuous layer, he has desig- 
nated as the parietal entoderm. He is followed in this by Wida- 
kowich. This nomenclature has been used by me in the sense 
employed by Sobotta. The parietal or transitory ectoderm 
(Kolster’s ‘feinfasserige Haut’) forming the roof or antimesome- 
trial portion of the vesicles, is constituted of a single layer of 
flattened cells, which in the rat show no regional differentiation. 
The resorption of maternal blood, incidentally noted with 
reference to cells of the ectoplacental cone and certain of the 
cells of the parietal ectoderm in connection with vesicle C of 
figure 24, to which phenomenon attention has been drawn by 
Sobotta and Kolster for the mouse, will receive further consider- 
ation in the discussion of older stages. 
DEVELOPMENT AND DIFFERENTIATION OF THE 
EGG-CYLINDER 
The material at hand is listed in table 8. 
TABLE 8 
RECORD NUMBER AGE NUMBER OF OVA 
17 8 days, 17 hours (?) 2 (not all cut) 
35 8 days, 18 hours (?) 6 
21 | 7 days, 16 hours 10 
66 7 days, 16 hours | <2 
27 7 days, 17 hours ff 
89 7 days, 20 hours 5 
81 | 7 days, 22 hours il 
94 |. 8 days 7 
95 8 days 9 
96 8 days ies 
For the stages showing the development and differentiation 
of the egg-cylinder in the albino rat I am able to present a series 
of stages which follow one another in close succession. The 
figures presented are in themselves so elucidative that an extended 
description is obviated. The stages under consideration fall 
within the eighth day after the beginning of insemination, 
judging from the great majority of the specimens at my dis- 
posal, although two rats (Nos, 17 and 35) killed in the latter 
