CASTES OF TERMOPSIS 527 



Imms ('19, p. 144) writes in regard to this question as follows: 

 ''I maintain that there is no satisfactory evidence conclusively 

 proving that any particular type of nutrition, or the absence 

 thereof, is capable of producing such fundamental changes in 

 the external and internal morphology which characterize the 

 soldier caste. It has also been shown that the reduction in the 

 gonads is not an invariable attribute of the soldier, and that caste 

 production is not in any way related to the presence of intestinal 

 protozoa." 



On pages 147 to 149 Imms ('19) discusses his view of the origin 

 of termite castes by mendelian inheritance from the winged sexual 

 forms : 



I propose to consider first a typical species of Termite comprising 

 monomorphic soldier and monomorphic worker castes and the ordinary 

 winged sexual forms. Let the symbols ASF represent the various alle- 

 lomorphs which express themselves collectively in the winged sexual 

 forms; F standing for the fertility determinant, and f for the absence of 

 that factor. The worker mutation I would explain as having arisen 

 by the loss of certain correlated allelomorphs, which we represent by S 

 and their absence by s. Similarly, by means of a second mutation, 

 involving the loss of another group of characters A, the soldier caste is 

 accounted for; the absence of A we will represent by a. The parental 

 forms will have the constitution AaSsFf , but the formula may be simpli- 

 fied by omitting the fertiHty determinant, which will be considered at a 

 later stage, since it bears no relation to the origin of caste. Now the 

 cross AaSs x AaSs affords an ordinary case in which two kinds of dif- 

 ferentiating characters are united, and the series contains nine different 

 forms among sixteen individuals (Bateson, '13, pp. 355 and 345). 

 These may be classified as follows: 



Soldiers Winged sexual forms Workers 



2 AaSS 2 AASS 2 AASs 



1 aaSS 4 AaSs 1 AAss 



2 aaSs 2 Aass 



Sterile gametic union 

 1 aass 



' The above hypothesis, involving the Mendelian inheritance of two 

 analogous mutations, appears to offer a simple explanation of the origin 

 of polymorphism among Termites. It, furthermore, accounts for the 

 persistence of castes, which are in themselves mostly sterile, securing 

 their representation in the germ-plasm of the species in each succeeding 

 generation. 



