74 



ELIOT R. CLARK 



nution of its angle of branching, as compared with that of branch 

 B, until, April 26, it forms, as it leaves the main stem A, almost a 

 direct continuation of A, while the angle formed by B is much 

 nearer a right angle. It will be noted that, in the later stages, 

 there is a reduction in the size of all the vessels. With this re- 

 duction, however, there is marked increase in rate of flow. Other 

 examples may be seen by comparing, in the successive stages 

 of the main series shown, the branches from the chief arteriole. 



Marl^' 



Mar.ZO 



Mar, li 



Apr. \3 



A}}r.Z6 



Fig. 15 Several stages of blood-vessels in the tail of rana sylvatica larva, 

 to show changes in angle of branching. In x, stage of April 26 is shown in dotted 

 lines, superimposed on stage of March 18. 



In these cases, the angle of branching is found to vary accord- 

 ing to the relative size of the branch — the larger the branch the 

 smaller the deviation from the line continuing the axis of main 

 stem, while the smaller the branch, the larger the angle — until, 

 when the disproportion is great, the angle reaches 90°. 



These results corroborate the results of Roux' studies, which 

 were based on measurements of arterial branches in adult animals. 

 Roux stated his results in the form of a law, namely, that the 

 size of the branch divided by the size of the main stem gives a 

 series of figures which vary about as the cotangent of the angle 

 of branching. He considered that the size of the angle represents 



