612 J. T. PATTERSON 
the thick embryonic ectoderm, curved upward on each side; (4) 
the thin amniotic ectoderm above; and finally, (5) the meso- 
derm of the false amniotic or extraembryonic cavity. 
Briefly stated then, each embryo consists of a tube-like out- 
_ growth from the ectodermal vesicle, with which it retains a 
Fig. 4 Outline reconstruction of the left half of specimen No. 170. Three sec- 
tions from this specimen are shown in plate 10, figures 75 to 77. x 62. 
connection in the form of the proximal part of the secondary 
bud. As a result of the manner in which the secondary buds 
arise from the primary ones, this connection is common to two 
embryos, which always constitutes a pair. 
Aside from the differentiation or organization of the embryos, 
the final stages in the extension of the secondary buds presents 
very little of special interest. We may therefore refer to them 
briefly. First of all, it should be stated that following a stage 
