CHAIN OF CYCLOSALPA AFFINIS 419 
the series of adhering foot-pieces is thus subjected results inevit- 
ably in a pulling apart of the foot-pieces somewhere. As a matter 
of fact the break produces groups and not single pairs. These 
groups then promptly shape themselves into the wheels. 
3. Comparison of the rate of growth of the chain as a whole with 
the rate of growth of other animals. As a matter somewhat to 
one side of the main problem, we have thought it worth 
while to compare the rate of growth of the chain as a whole with 
what is known of the growth of other organisms. This was done 
by the method employed by Minot (’91) in his study. of the rate 
of growth of guinea pigs; namely, by finding the per cent of increase 
throughout the chain. The values of the corresponding zooids 
of Chains I, II, III, VI, and VII were averaged. (Chains IV 
and V being so much shorter were omitted.) The per cent of gain 
of the second over the first, third over the second, etc., was then 
computed and the values plotted. The result is a very ragged 
line showing a gradual increase through two-thirds of its length 
and a more sudden drop at the end. To get a graph whose course 
was more evident, the increment was computed again, this time 
taking the series in groups of five. The first value here is the 
per cent of increment of the second five over the first five, ete. 
(table 4, fig. 9). The gradual increase, maximum toward the 
end, and rapid decline is here plainly shown in spite of the limited 
data. 
This result seems strikingly different from that for the guinea 
pig and other animals of higher order, where the per cent of in- 
crement is a diminishing one from birth on. The difference may, 
however, be more apparent than real since, to make the compari- 
son more correct, it would seem that stages in the mammalian 
development preceding birth would have to be used. 
The drop in rate of increase, when the wheel part of the chain is 
reached, may be significant for the comparison, but we do not 
consider our observations carried far enough into the life of the 
chain as a whole to warrant any speculation based upon them. 
A study of the growth of still younger and still older, larger zooids 
will have to be made to meet the requirements here. 
