CHAIN OF CYCLOSALPA AFFINIS 423 
Frequency. 
15| /6| 
Fig. 10 Frequency polygon showing the number of zooids in the wheels 
No. of zoo/ds... Half Wheel. Whole Wheel, 
wheel, so that in the fully grown wheels the zooids are held together 
almost entirely by the peduncles. The observed facts certainly 
suggest group adherence among the foot-pieces themselves. Can 
direct evidence of any such thing be obtained? 
Having proved the existence of a pronounced size grouping of 
the zooids in the wheels it naturally occurred to us that there may 
be something of the same sort in the peduncles and foot-pieces. 
We consequently made a considerable number of measurements 
on these structures. Some of the numbers are given in table 5, and 
in fig. 1; the graphs of peduncle lengths (dotted line) and foot- 
piece lengths (lower continuous line) are presented. It is doubt- 
ful if these show anything. We have not assumed that they do. 
The difficulties in the way of making the measurements are too 
great for the methods employed. It should, however, be borne 
distinctly in mind that these negative results prove no more than 
the insufficiency of the measurements. The fact that the foot- 
pieces do cling to one another in groups, and that the zooids to 
to which they belong are demonstrably different in size, appears 
to make it probable, a priori, that the adhesive power of the foot- 
pieces is of the gradational, or periodic sort, in spite of our failure 
to find it. The suggestion is that the graded size of the zooids 
is reflected in the adhesive power of the foot-pieces. Could this 
