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 



