17 
The OCCASIONAL PHENOMENAL ABUNDANCE 
of CERTAIN FORMS of INSECT LIFE. 
Jaxv Wo Ith Slalalasle’, 
[Read 11th November, 1892.] 
THE subject of the present paper 1s one which appears to 
me to merit the attention of all biologists. The phen- 
omenon of the greater or less abundance of individuals 
of any particular species at different times extends 
throughout the whole of animal life and is indeed one of 
the most obvious facts of nature. As might have been 
expected this waxing and waning of vitality is most 
obvious and most emphatic in those groups whose vital 
economy is most delicately adjusted to their environment. 
Of course also the shorter the individual life and the 
greater the capability of increase, so much the greater is 
the possibility and indeed the actuality of extreme irregu- 
larity of survivals. Thus the phenomena of which I am 
treating is found most obtrusively noticeable among the 
Insects, both because that group comes more immediately 
and constantly under notice, and because while the capabil- 
ity of racial increase is very large, the span of individual life 
is usually very short rarely indeed more than annual, or 
at best biennial. JI think I might also add that the fact of 
the extreme disparity between the various states of insect 
embryonic development renders that class more hable to 
fluctuations of survivals, because the relations between 
the individual life and the environment are necessarily so 
much the more complex and variable. 
That this phenomenon of sudden and unexplained 
abundance is not unknown among even so highly devel- 
