DEVELOPMENT OF EMBRYO OF FOWL. 5 I 



It will be seen (Fig. 10) that this operation has taken us in 

 front of the vitelline arteries ; having been performed before the 

 development of the arteries, it was possible for the rudiment of 

 the vascular system to readjust itself to the new conditions, and 

 establish a vitelline circulation. The vitelline arteries are, how- 

 ever, in about their normal position, i. e., about opposite the 20-22 

 somites, hence behind the embryo in this case. It is difficult to 

 see why they should have this position and not be shifted farther 

 forward, if the view of His, that the main blood vessels develop 

 from the paths of least resistance in the primitive vascular net- 

 work, be true. 



On the right side of this embryo there are 14 spinal ganglia, 

 and on the left 14 complete and part of the fifteenth ; but as, in 

 the fowl, the first two cervical nerves lack ganglia, there are 

 present 16 spinal nerves on the right side, and 17 on the left. 



X 



FIG. 10. Defective embryo (experiment 187). The drawing was made from 

 the stained and cleared specimen. A, vitelline artery ; V, vitelline veins ; W, wing 

 bud ; X, sac filled with blood, behind the embryo in the prolongation of its axis ; 

 this has no connection with the vessels of the embryo. 



The normal innervation of the wing is from the fourteenth to 

 the sixteenth spinal nerves. It would thus appear, on the evi- 

 dence of the nerves, that the operation has destroyed everything 

 back of the wing somites. The wing -buds have a development 

 that appears perfectly normal for this stage. 



