INTRODUCTION i9 
In the Arctic regions we find vast numbers of individuals of 
but few species, whereas in the tropics the individuals are little or 
no more numerous, but the number of species much greater than 
in cold regions. 
It is a mistake to assume that animals invariably become rarer 
as we approach the limit of their range; for example, the common 
scallop is very abundant in Provincetown Harbor, Cape Cod, but is 
all but unknown north of that place. ‘ 
An interesting account of the distribution of deep sea animals, 
and of the floating life, is given by Alexander Agassiz in “Three 
Cruises of the Blake,” 2 vols., 1888, Bulletin of Museum of Com- 
parative Zoology at Harvard College; and a very general discussion 
of the distribution of animals as a whole is given by Professor A. 
Heilprin in ‘The International Scientific Series,’ Vol. LVII, 1887. 
The study of intelligence in lower animals is a subject of fas- 
cinating interest. Nevertheless popular writings upon such mat- 
ters are usually in error, for the authors are too apt to conclude 
that when the actions of an animal appear “sensible” from our 
point of view, or evidently serve a useful purpose, they must 
necessarily be conscious. For example: the caterpillar of the mon- 
arch butterfly (Danais arehippus) feeds only upon milkweed, and is 
generally found upon the tender young leaves near the top of the 
plant, where it is surrounded by the juiciest and most nutricious 
food. [xperiments by the author show, however, that we can not 
conclude that the caterpillar exercises any conscious choice or 
reason in the matter, for its being there is due to two simple reac- 
tions. It has an inborn tendency to crawl upward rather than down- 
ward, and it is also strongly inclined to crawl toward the hght. If 
one plant a milkweed in a flower-pot, and then turn it upside-down 
the caterpillars will soon crawl upward toward the light of the sky, 
and will thus wander away from the plant and starve to death, 
although under normal conditions these two reactions would serve 
to maintain them in the best situation for obtaining food, and pre- 
vent their roaming away from the plant. 
Nagel and Parker have also shown that if we place a piece of 
meat upon certain of the tentacles of a sea-anemone, the meat is 
rapidly thrust into the mouth. If then we place a piece of paper 
soaked in a weak solution of meat juice it is at first swallowed, but 
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