428 W. E. RITTER AND M. E. JOHNSON 
the individual blood vessels are arranged at regular intervals along 
the large vessel. The arrangement is the same for the first wheel, 
but with the second or third wheel the axial vessel begins to shrink. 
As the vessel remains in connection with the individual lateral 
vessels, while growing smaller, it comes to have a zig-zag course, 
due to the opposite but alternate pulls upon it by the growing zo- 
oids. The shrinkage of the vessels goes on so rapidly and to such 
an extent that in the next wheel the vascular connection between 
the central zooids is lost. The portion of the main vessel which 
joins two wheels together persists for some time. In fact this and 
the transparent cellulose envelope which forms around the wheels, 
filling in the spaces between the zooids, are all that hold the chains 
together and very long chains of wheels aresometimesfound. The 
small remnants of the individual vessels gradually disappear. 
Though these vessels end blindly, the blood may still be seen in 
them forsome time, flowing out one side and back theother. After 
the disappearance of the main vessel at the center of the wheels, 
short circuits are maintained between the zooids connected at 
any point. Thus in fig. 18, zooids 1, 2, 12, 6', and 7! have a circuit 
of theirown. Thus it would seem that if any of the zooids of the 
wheels have an advantage over others the end ones would be fa- 
vored as against the middle ones, but the middle ones are on the 
whole larger. Hence inequality in blood, supply seems to be 
excluded from being a determining factor in the size relations 
observed. 
If there be any communication between the zooids of the un- 
broken chain or of the wheels, other than by the circulatory sys- 
tem just described, it must be through the peduncles. The ves- 
sels in the peduncles are irregularly arranged but they are dis- 
tinctly larger toward the edges and reach part way into some of 
of the papillae. They are easily followed in the living specimens. 
To test the question of blood communication between zooids, 
injections were made. Methylene blue in sea water was used, 
which could plainly be seen in the transparent peduncles and in 
the bodies of the salpae. The first attempt was on two wheels 
whose stage of development was the same as the third and fourth 
in fig. 18. The needle was inserted in the stolonic vessel half way 
