DEVELOPMENT OF THE ALBINO RAT 339 
the primary embryonic entoderm. The portion of the visceral 
entoderm surrounding the sides of the egg-cylinder in the region 
of the extraembryonic ectoderm, to near the base of the ecto- 
placental cone, consists of a single layer of columnar cells, regu- 
larly arranged and presenting the three zones described by So- 
botta. In this stage of egg-cylinder development of the albino 
rat, the absorption of hemoglobin granules derived from maternal 
blood cells, first shown for the mouse by Sobotta and Kolster, 
may be readily made out. In preparations stained in hematoxylin — 
and Congo red, in and on the outer zone of the visceral entodermal 
cells there may be observed granules staining deeply in the Congo 
red, presenting the color reaction of hemoglobin. In the mid- 
dle zone of these cells the protoplasm is distinctly vacuolated, 
while the inner zone, containing the nuclei, presents a denser 
protoplasm. The transitory or parietal ectoderm consists of a 
homogeneous membrane, closely adherent to the maternal de- 
cidua, especially along the sides of the egg-cylinder. This layer 
presents scattered nucleated protoplasmic masses of spindle or 
dome shape on its inner surface, the relations and distribution 
of which may be clearly seen in the figure. Attention needs 
yet be drawn to the ectoplacental cone of the egg-cylinder. Its 
relation to the maternal decidua is very intimate, so that in 
places, owing to blood extravasations, it is difficult to differentiate 
between embryonic and maternal tissue. Many of the cells 
of the ectoplacental cone present a vacuolated protoplasm, the 
vacuoles enclosing maternal blood cells. Therefore, they are 
distinctly phagocytic. Sobotta has also observed and described 
this for the mouse. Referring to a slightly older stage after the 
anlage of the mesoderm, his own words read as follows: 
Weiterhin sehen wir im Stadium der Fig. 5 auch eine starke Ver- 
langerung und Vergrésserung des Ectoplacentarconus, an dem im meso- 
metralen Teile jetzt Vacuolen auftreten, die in spateren Stadien regel- 
massig gefunden werden und zwar erfillt mit miitterlichen Blutex- 
travasaten. Die Ebrnaihrung des Embryo mit miitterlichem Himo- 
slobin * * * * ist jetzt im vollen Gang. 
Absorption of maternal hemoglobin by the cells of the ecto- 
placental cone appears to be established at a relatively earlier 
period in the rat than in the mouse. 
