432 W. E. RITTER AND M. E. JOHNSON 
of a systematic character among the zooids of the chains. It 
was only from certain biological considerations combined with 
aid from this instrument, that the existence of the system was 
made certain. And it should be specially noted how our results 
would have been affected by failure to recognize this fact. The 
breaking up of the chain 7n some way, and the production of wheels 
from the breaking, could have been inferred from the unequal 
growth of the bodies and foot-pieces of the zooids; but why the 
breaking should be into groups rather than into single pairs would 
have remained with no definite answer but for the discovery of 
the periodicity in growth in the unbroken as well as in the broken 
part of the chain. 
2. Natural periodicity in organisms and exacter methods of 
research 
But promptly comes the question from some of the foremost 
biologists, What of it? What particular good is there in knowing 
that growth is periodic so long as we have no explanation of why 
it is so? Our real interest, they say, is in the causes not the mere 
facts of organic phenomena. ‘This objection displays, in our opin- 
ion, one of the most pervasive and fundamental weaknesses in the 
biological philosophy of the day. Looked at critically, it is found 
to mean that facts of nature, in order to be interesting and 
deemed really worth while, must be prejudged; that an explanation 
of them must be ready at hand before they are observed in order 
that they may be attractive. The issue must be looked squarely in 
the face. It is in fact the old, old issue between the inductive 
and the deductive methods of interpreting nature; between ob- 
servation and reason going hand in hand, and the power of reason 
alone; between the a posteriori and a priory modes of reasoning. 
The objection carries the implication that great numbers of facts 
of nature can be explained without having been themselves ex- 
amined; that the unobserved causes of many observable effects 
may be sufficiently inferred from observations on other effects 
than the particular ones under consideration. In a word the 
meaning is implied if not expressed, that some time nature may 
