VASCULAR AREA OF CHICK BLASTODERM. 87 



Experiment IV. The foregoing experiment shows conclusively 

 that the differentiation of one part of the vascular area does not 

 depend on the previous development of another part. It does 

 not answer the question, however, as to whether the develop- 

 ment of the vascular area is dependent on the progressive differ- 

 entiation of the embryo. There are a number of ways (experi- 

 ments) by which one can prevent the development of the embryo, 

 and at the same time show that the primordium for the entire 

 vascular area is laid down irrespective of the differentiation of 



FIG. 5. Photograph of the resulting embryo in Experiment II. The opera- 

 tion was made on the unincubated egg (see Fig. i, B), and the egg was then 

 incubated for forty-nine hours. While development has been greatly delayed, 

 yet the embryo proper is normal, and eight somites are formed. X 12. 



the embryo beyond the primitive streak stage. One of the 

 simplest of these is shown in Fig. I, D, and the resulting blasto- 

 derm in Fig. 7. Although there is not the slightest trace of the 

 embryo proper present, yet the vascular system of the area opaca 



