84 Bulletin American Museum of Natural Historij. [Vol. XXIII, 



isms are far and away the most plastic and adaptable and psychically the 

 most richly endowed of all the lower animals. I use this term "psychically" 

 advisedly, for, like Forel and Wasmann, I find myself utterly unable to 

 accept the views of Bethe, Uexkiill, and others, who regard the social insects 

 as mere reflex machines. Nor have I the slightest hesitation in substituting 

 psychological terms wherever physical terms are inadequate, as I am by no 

 means convinced of the cogency of the hypothesis of psychophysical par- 

 allelism and the epistemological restrictions to which it is supposed to bind 

 the investigator. If I am not greatly mistaken, psychophysical parallelism 

 has of late received some pretty rough treatment at the hands of more than 

 one eminent psychologist.^ 



As the type of polymorphism with which I have been dealing has been 

 developed by psychically highly endowed social insects, it cannot be ade- 

 quately understood as a mere morphological and physiological manifestation 

 apart from the study of instinct. This has been more or less distinctly per- 

 ceived by nearly all writers on the subject. However various their expla- 

 nations, Spencer, Weismann, Emery, Forel, Marchal, and Plate all resort to 

 instinct. Emery, especially, has seen very clearly that a worker type with its 

 peculiar and aberrant characteristics could not have been developed except 

 by means of a worker-producing instinct. In other words, this type is the 

 result of a living environment consisting of the fostering queen and workers 

 which instinctively control the development of the young in so far as this 

 depends on external factors. Only under such conditions could a worker 

 caste arise and repeat itself generation after generation. This caste may 

 be regarded as a mutation, comparable with some of De Vries's Oenothera 

 mutations, but able to repeat and maintain itself for an indefinite series 

 of generations in perfect symbiosis with its parent form, the queen, because 

 notwithstanding its relative infertility, it can be put to very important social 

 use. Among ants this social use not only pervades the activities of the 

 adult worker but extends even to the more inert larval stages. Thus the 

 latter represent a rich and ever-fresh supply of food that can be devoured 

 whenever a temporary famine overtakes the colony. In certain species, 

 like the East Indian (Ecophylla smaragdina and the South American 

 Cainpo7iofufi sene.v, the larvae are put to a more humane use as spinning 

 machines for constructing the silken nest inhabited by the colony. These 

 examples also illustrate the purposive manner in which an organism can 

 satisfy definite needs by taking advantage of ever-present opportunities. 



In the lives of the social insects the threptic, or philoprogenitive instincts 

 are of such transcendent importance that all the other instincts of the species, 



^ 1 See, e. g., Biisse, Geist und Korper. Leipzig, Diirr'sche Buchhandlung, 1903; and Binet, 

 L'Ame et le Corps. Paris, Ernest Flammarion, 1905. 



