Experimental Entomology. Factors in Seasonal 
Dimorphism, 
by F. MERRIFIELD, F. E. S. (London). 
I felt considerable diffidence when invited to take a part in one 
of the sectional meetings of this important international gathering 
of entomologists, but was informed that it was desired that experi- 
mental entomology should be represented, and as this is one of the 
few subjects connected with entomology on which I have had 
some experience, though little as compared with that of others such 
as STANDFUSS, FISCHER and BACHMETJEW, who are prevented 
from being present, I have ventured to do so. It is not necessary 
for me in this assembly to dwell on the importance of the experi- 
mental side of observation in reference to the many problems that 
present themselves to investigators into the reasons why organisms 
come to be what they are. That their structure and their life 
habits are owing mainly to the external conditions to which they 
or their ancestors have been subjected may be taken as a fact. But 
the external natural conditions and the internal adaptabilities of 
the organisms are so numerous, so complicated and delicate, so 
varied and so mingled together, that, in order duly to appreciate 
cause and effect, it is absolutely necessary to resort to the means 
which experimental work affords of isolating different factors, and 
thus learning by which of them the results we see have been 
brought about. Isolation is the necessary means for unravelling 
the tangles presented by nature, many of them very beautiful, but 
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