DEVELOPMENT OF VESSELS WITHOUT HEART 



183 



In all of the chicks operated upon, with the exception of the 

 ones that failed to survive the operation, the vessels of the extra- 

 embryonic region were filled with red blood cells, which made 

 them clearly discernible before the injection. These vessels, 

 during the first two or three days after operation, were injected 

 without especial difficulty, the injection mass spreading out uni- 

 formly from the point of injection. In later stages, however, 

 increasing difficulty was encountered, the ink often going but a 

 short distance. This difficulty proved to be due to the irregular 

 narrowing and retraction of the vessels which occurs in later 

 stages. 



That the area vasculosa continues to grow and expand after 

 the operation is certain, and the results of a number of measure- 

 ments upon operated chicks are reported in tabulated form be- 

 low as compared with normals at the time of operation and later. 



SPECIMEN 



Area vasculosa, .33 hours 

 Area vasculosa, 106 hours 

 Area vasculosa, 105 hours 

 Area vasculosa, 8§ days. 

 Area vasculosa, 8 J days. 



Embryo, 4^ days 



Embryo, 4| days 



Embryo, 41 days 



REMARKS 



Normal chick 

 Operated chick 

 Normal chick 

 Operated chick 

 Normal chick 

 Operated chick 

 Operated chick 

 Normal chick 



It is apparent from this table that while there is a surprising 

 amount of peripheral extension of the area vasculosa in the op- 

 erated chicks, still the growth is less than half as rapid as in the 

 normal chicks. The embryos showed a similar difference. A 

 number of operated chicks measured approximately 6.5 mm. in 

 length as compared with a normal embryo of the same age, which 

 was 13 mm. in length. 



The area vasculosa of the operated chicks did not always ex- 

 pand uniformly in each direction, as in the normal, but often 

 grew out at certain points, usually posteriorly from the embryo, 

 in advance of other portions. Figure 2 is a diagram of one of 



