POLYMORPHISM IN NEUTER INSECTS 65 



than for length ; Alpatov (1930) rinds the same phenomenon. 

 Smirnov and Zhelochovstev (I.e.) for the blowfly Calliphora find 

 a differential effect in different regions of the wing when total size 

 is reduced by cutting off larval food-supplies after a given time. 

 On the other hand, Alpatov (1. c.) in flies of the same species 

 reduced in size by depriving larvae of food before they reached 

 full growth, also finds a decrease in relative breadth of the 

 wings, showing that absolute size is not the only factor deter- 

 mining proportions. 



When, as in some more specialized forms, the neuter series 

 is not continuous, but there exist only two or a few fairly 

 sharply defined types — e.g. only large and relatively large- 

 headed soldier and small and relatively small-headed worker — 

 we need only suppose a slight specialization of the nurses' 

 behaviour. An adumbration of this is seen in the fact, elicited 

 by unpublished work of Miss Edmonds, of Sydney, that even 

 in forms with a continuous series of neuters, the frequency 

 curve for body-size is definitely multimodal (see also Palen- 

 itschenko, 1927). 



It is to be hoped that those familiar with the technique 

 of rearing ants in captivity will attack this problem experi- 

 mentally. If my suggestion be verified, it will materially 

 simplify the evolutionary problems connected with the poly- 

 morphism of ant neuters, for instead of having to postulate a 

 large number of genetically distinct types, we need only assume 

 one single genetic type of neuter, but provided with a heter- 

 ogenic mechanism for head-growth, which will produce all 

 the different head-types as secondary by-products of the 

 animals' absolute size. 



In termites, the case is somewhat different. 1 Within the 

 soldier caste of primitive termites, we do sometimes meet 

 with phenomena which appear to be quite parallel with what 

 I have discussed for ants — considerable variation in absolute 

 body-size accompanied by a progressive alteration in relative 

 head- and jaw-size. This is well shown in the figures given by 

 Heath (1927) ; see Fig. 38. Heath also (see his p. 402) demon- 

 strates fairly conclusively the interesting fact that the poly- 

 morphism is due to the presence of forms which have gone 

 through different numbers of moults ; a fact which strengthens 

 our hypothesis that there is but one genetic type with a heter- 



1 For much of the information concerning termites I am indebted 

 to Professor A. E. Emerson, of Chicago University, to whom I should 

 here like to express my thanks. 



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