412 W. E. RITTER AND M. E. JOHNSON 
were reversed for fig. 8 so that values greater than the correspond- 
ing ones in the fitted curve lie above the x axis while smaller ones 
lie below. Vertical dotted lines have also been drawn to indicate 
a possible grouping of the zooids. Irregularities appear, it is true, 
but since irregularities often appear in the wheels also it is to be 
expected here. Moreover, with such small values the chances 
for error are so great that one would expect considerable variation. 
46 50 54 58 62 66 70 74 78 62 86 ao) 
Plot of Differences 
Chain VI... Right side. 
Upper series... 45-90. 
Lower series..... 1-45. 
ER SEER Gee EB ENBee 
Rae AGee Gare BERANE A eee 
Pa aN aL Nat RR I al a 
eae Re See t 
Soe a 
EEEEEEEEE EE He AP 
| 
al 
(eS A a 
ial cae 
Ce 
Mono IAD 
ELE Reae 
DR Sree r 
fe) es a 
2 6 10 14 18 22 Zola, «34. Gap ae cas 
Fig. 7 Plot of differences for chain VII, right side 
What we get then from these plots of differences is the probable 
fact that the unbroken part of the chain really shows a periodicity 
or incipient grouping closely resembling that of the wheeled portion 
of the chain, the groups including four to eight zooids each, which 
is the number found in the completed wheels. 
The plots of differences brought to light an aspect of the matter 
which had not been anticipated, namely, the existence of another 
wave with a longer period, shown in all the curves. The plots in 
