CHAIN OF CYCLOSALPA AFFINIS 435 
of organisms, dealt with. Yet how these writings bristle with 
such expressions as ‘differs considerably,’ ‘constant results.’ 
‘as a rule,’ ‘very similar,’ ‘normal segmentation,’ ‘normal nuclear 
spindle,’ ‘normal blastulae,’ ‘normal animal,’ ‘practically iden- 
tical,’ ‘essential features,’ ‘increases in exact proportion,’ and so 
on! 
Two rejoinders are frequently made to this demand for carry- 
ing more exact methods into biology. One is on the purely theo- 
retical ground that it is not necessary; that ‘mere quantity’ is of 
no great moment in life phenomena; that slight differences are 
of the purely ‘fluctuating’ or individual sort, so have no large 
significance. ‘To answer this objection in full would take us much 
farther into philosophical discussion than we can go here, but it 
may be the more warrantably passed by because the attitude of 
mind that makes it is seen to be obviously hostile to the whole 
trend and spirit of physical science. If the history of progress 
in science can be relied upon to furnish any clue as to how progress 
is to be continued in the future, the man of science, who holds a 
general view of nature that makes many facts insignificant and 
negligible, is bound to come to grief sooner or later. 
The other objection is more practically justifiable. It is that 
the phenomena of living beings are so complex and subtle, 
and that animals, especially, are so sensitive to changes in exter- 
nal conditions as to make it impossible to apply to them in more 
than a very limited way, the exacter methods of the physical 
laboratory. Our answer to this is two-fold. In the first place, 
we are persuaded that exact methods could be applied far more 
widely than they are, and they undoubtedly would be, did our 
general conceptions call for such applications. The other an- 
swer is that if it be true, as it well may be, that many life processes 
are too subtle and involved to submit to measurement on an 
exact and large scale, then the only course open for the inter- 
pretation of such processes is to introduce no considerations that 
envolve the conception of accurately measured quantity. The ex- 
tent to which this principle, seemingly so obvious and unes- 
capable, -has been violated in much biological theory during 
the last quarter century or more, is seen to be remarkable once 
