PHYLOGENETIC ORIGIN OF TERMITE CASTES. IIQ 



The question that presents itself to our minds is, therefore, 

 in which of these two categories of variations do the termite 

 castes belong? or, in other words, are the castes of termites, 

 both in origin and at present, to be considered as fluctuating 

 variations or as mutations? 



Several lines of approach lead toward the solution of this 

 problem: (i) the study of fossil insects, from the Cretaceous 

 period when termites are said to appear 1 up to the present time ; 

 (2) the comparative morphology of the order of termites; (3) 

 exact field observations upon termite biology; (4) breeding expe- 

 riments to determine the type of progeny and the results of 

 hybridization. 



None of these lines of work have been thoroughly or exhaus- 

 tively investigated, and the gaps in our knowledge are very wide. 

 There are, however, a few scattered observations, to be summar- 

 ized in this paper, drawn partly from the literature of the social 

 insects, and partly from the field and laboratory studies of the 

 two authors, which may be of value in the attempt to solve the 

 problem of the variations known as termite castes. 



In a recent paper, Wheeler (1917) has stated his opinion that 

 the castes of ants represent continuous, i. e., fluctuating varia- 

 tions. This view is based upon the study of the fossil ants of 

 the Baltic amber, and upon comparative morphological data. 

 "In most species of ants the constant and striking structural 

 differences between the different castes would, at first sight, 

 suggest that such forms as the apterous females, apterous males, 

 soldiers and workers, must have arisen as so many saltatory 

 variations, or mutants and that they survived and secured 

 representation in the germ-plasm, because they happened to 

 fulfill specialized and useful functions in the life of the colony. 

 I believe, however, that this view of the castes, at least so far 

 as their origin is concerned, cannot be maintained, because all 

 the available evidence points to their being merely the surviving 

 extremes of graduated and continuous series of forms, the annec- 

 tant members of which have suffered phylogenetic suppression or 

 extinction." 



Handlirsch (1908), p. 1191, states that the number of termite 

 genera was far greater in the Tertiary period than at present. 



1 Handlirsch (1908). 



