396 W. E. RITTER AND M. E. JOHNSON 
The larger significance /of such studies... .c. ca sel ee es ee eee 431 
1. Supplementing biological with quantitative observations ............... 431 
2. Natural periodicity in organisms and exacter methods in biological re- 
[a 46) | a nes lt ea ane hae aarlee TOMA EAN MIA Rien ty cialis te 5 432 
3. The inadequacy of treating periodicity, generally, as an aspect of fluc- 
PUAtINS, VATIGUION Ay eae |. c : forsse Dek Soy aes see ie eels oe Meenas eee 440 
Bibliography £20 24-i2stad seme Oboe 6 «i tiouc netic 5 tee atte 9 wre G2 re tS one fe eee 444 
PURPOSES OF THE RESEARCH 
1. Special 
One of us (Johnson, 710) has shown that the individuals of the 
blocks into which the chains of blastozooids of Salpa fusiformis- 
runcinata, S. cylindrica, and 8. zonaria-cordiformis become dif- 
ferentiated, fall into size schemes, or systems. 
The question naturally arises, how general is this phenomenon 
among salpae? The possibility that the wheel grouping in Cyclo- 
salpa corresponds to the block grouping in Salpa proper, occurs to 
one rather readily in spite of the conspicuous differences between 
the two. If this conjecture be right, we should expect to find a 
size scheme of zooids in the wheels of Cyclosalpa similar to that 
in the blocks of Salpa. That such a scheme exists in the wheels 
even more pronouncedly than in the blocks, the sequel will show. 
2. General 
This much more evidence is consequently adduced favorable 
to the idea of correspondence between the wheels and the blocks. 
But what do we mean by correspondence? In a general sense the 
blocks and wheels undoubtedly correspond: both are groups of 
similar organisms similarly located with reference to the parent 
zooid. This much of correspondence is recognizable to cursory — 
inspection. Does the discovery of a similar size scheme among 
the zooids in the groups in the two species advance our interpreta- 
tion of these organisms much if at all? Does it amount to any- 
thing more than a recognition of one more resemblance? Accord- 
ing to the meaning that ‘interpretation’ and ‘resemblance’ have 
in most later biological writing, we must probably say no. We 
