84 G. CARL HUBER 



brane derived from the parietal or transitory ectoderm and the 

 scattered cells forming the parietal layer of entoderm. This 

 membrane is continuous with the base of the ectoplacental cone 

 and presents scattered flattened cells on its inner surface. I have 

 designated this thin membrane with cells on the inner surface 

 as the parietal or transitory ectoderm (Kolster's feinfaserige 

 Haut). The egg-cylinder which extends to the antimesometrial 

 end of the yolk-sac cavity, encloses the proamniotic cavity, the 

 antimesometrial portion of which is walled by primary embryonic 

 ectoderm, its mesometrial portion by extraembryonic ecto- 

 derm, the two forming a continuous layer, with line of union 

 of the two types of ectoderm evident. The uncleaved extra- 

 embryonic ectoderm is continuous with the base of the ecto- 

 placental cone. The egg-cylinder is surrounded by a single 

 layer of cells of the visceral entoderm, differentiated so as to 

 consist of a portion which surrounds the antimesometrial end 

 of the egg-cylinder in relation with the primary embryonic ec- 

 toderm; the cells of this portion being of a rather thick pavement 

 type, constituting the primary embryonic entoderm, and fur- 

 ther a portion which covers the sides of the egg-cylinder, with 

 cells of a columnar type, showing special cytomorphosis. The 

 egg-vesicles and egg-cylinders of the stage of development under 

 consideration and for somewhat older stages show no bilateral 

 symmetry so far as can be discerned by study under the micro- 

 scope. In longitudinal sections of egg-cylinders, cut respectively 

 in two different planes, at right angles to each other, no differ- 

 ence in form, relation and structure of different parts can be 

 observed. Selenka, Kupffer, Duval, and Sobotta have pre- 

 viously called attention to this fact and shown that longitudinal 

 sections of egg-cylinders may be obtained no matter whether 

 the sections are cut parallel to the plane of the mesometrium, 

 thus parallel to the long axis of the uterus, or at right angles to 

 this plane. The want of bilateral symmetry is also evident in 

 cross sections of the egg-cylinder, as may be seen from the 

 series of sections presented in figure 28 (rat No. 27, 7 days, 17 

 hours). The cross-cut egg-cylinder, from several sections of 

 which these figures were drawn, represents a stage of develop- 



