CHAIN OF CYCLOSALPA AFFINIS 427 
the small groups appear to be more irregular on account of their 
riding on the secondary waves, they are of the same sort. It 
must be remembered, too, that the values are very small and 
the chances of error are large. In fact, such a uniformity of re- 
sult throughout all the graphs examined, in spite of small values 
and difficulty of measurement, is very convincing. 
The transformation of the groups of zooids into wheels is easily 
understood: The moment the break occurs so that the pressure of 
the zooids upon one another in the group canexertitseffect back- 
ward as well as forward, the hindmost pair swings in toward the 
axial line, each of the other pairs up to the transverse middle line 
of the group following in its proportional amount. Since by this 
time the foot-pieces have wholly or almost wholly disappeared and 
the central ends of the peduncles have become closely appressed, 
the swing of the zooids disposes the peduncles in the form of the 
spokes of a wheel, the hub being represented by a small elliptical 
space. The course of things here described is illustrated in fig. 17. 
That the pressure tending to force the mid-zooids of the groups 
outward is considerable is obvious from the zig-zag form into which 
the axial vessel is thrown, due to the pull on the radial vessels, 
as seen in the second group of fig. 18. The disappearance of the 
axial vessel in the older wheels may be supposed to be partly due 
to the same cause, although probably the vessel is actually 
in course of degeneration. 
3. Impossibility that the character of the blood supply to the zooids 
can be the cause of the size schemes within the wheels 
No study involving the growth of the zooids could be complete 
without attention having been given to so fundamental a matter 
as that of the blood supply. For example, the question naturally 
arises, does not the break-up of the chain into groups so affect 
the common blood vessel of the stolon that the zooids do not 
share alike in nutriment received, and is not this inequality respon- 
sible for the disparity in size among the zooids? 
The changes in the circulatory system are best shown by the 
diagram fig. 18. At the end of the continuous part of the chain, 
JOURNAL OF MORPHOLOGY, VOL. 22, NO. 2 
