The Location of the Chick Embryo. 



373 



mined to find out, if possible, whether the embryo would form on 

 any other part of the blastoderm if development on the radius x-y 

 was prevented. 



Experiment II. The blunt end of the egg was held in the left 

 hand so that the blastoderm lay on top of the yolk; a small window 

 was made immediately above it, and a series of injuries were made 

 with a hot needle in the radius x-y. The number of injuries was 

 dependent upon the size of the area pellucida. Usually there is 

 space enough to insert the tip of a No. 12 cambric needle in three 

 places between x and y (Text-fig. 6) before all the cells are 

 destroyed. 



At the end of eighteen hours the eggs were killed, but no trace 

 of primitive streak in another region was found. About 60 per 

 cent, of the blastoderms showed a large hole where the area pellu- 

 cida had stretched apart in the growth of the blastoderm. No 



5 6 



evidence of the formation of the embryo around the margin of the 

 hole could be found. 



The experiment was repeated and the eggs were incubated 

 from thirty to forty hours. An examination of these embryos 

 showed no development around the margin of the wounded area, 

 but in front of it and posterior to it some development had taken 

 place. In PI. I, Fig. 3, a surface view of an embryo of forty hours' 

 incubation is given. The brain is abnormal, but shows no lack 

 of material, the notochord is present, but greatly reduced in 

 length. There is some trace of the heart lying on each side of the 

 notochord, but back of it none of the embryo has formed. There 

 is no evidence of growth of the area pellucida in a posterior direc- 

 tion, but anteriorly it is the normal size and shape. 



Another embryo incubated thirty hours is shown in PI. I, Fig. 

 4. In this embryo no brain developed but growth from the heart 



