INTRODUCTION 19 



In the Arctic regions we find vast numbers of individnals of 

 but few species, Avliereas in tlie tropics tlie individuals are little or 

 no more numerous, bnt 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 Avhole 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 fDanais areltippusj feeds only upon milkweed, and is 

 generally found upon the tender young leaves near the top of the 

 plant, whore it is surrounded by the juiciest and most nutricious 

 food. Experiments 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 light. If 

 one plant a milkweed in a ilower-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 



