328 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-sae 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- 
