DEVELOPMENT OF THE ALBINO RAT 95 



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 Vergrosserung des Ectoplacentarconus, an dem im meso- 

 metralen Teile jetzt Vacuolen auftreten, die in spateren Stadien regel- 

 massig gefunden werden und zwar erfullt mit miitterlichen Blutex- 

 travasaten. Die Ehrnahrung des Embryo mit miitterlichem Hamo- 

 globin * * * * 1st 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. 



