66 



PROBLEMS OF RELATIVE GROWTH 



ogonic mechanism as regards head-size. The different soldier 

 forms are discontinuous as regards size and head-proportions, 

 which provides us with a further case of di- or poly-morphism 

 due to a combination of heterogony with moulting (§ 5). 

 Reference may also be made to some of the results given in 

 the important paper by Kalshoven (1930), and in that by 

 Hare (1931). Such a method of arriving at polymorphism of 

 neuters would, of course, be impossible in the holometabolous 

 ants. (See also the work of Light, p. 258.) 



There are however other termite cases in which my hypo- 

 thesis would not seem to apply. For in- 

 stance, A canthotermes acanthothorax (Sjostedt, 

 1925 : his Fig. 21, p. 61) has certainly two 

 qualitatively different types of soldiers, which 

 it would appear necessary to regard as differ- 

 ent genetic types, or at least as produced by 

 qualitative differences in feeding. Sjostedt 

 himself figures no less than five kinds of 

 soldiers, the largest number of types decribed 

 for any species of Termite. Two of these, 

 his Nos. 4 and 5, would appear to be growth- 

 forms of one main type. To inspection, his 

 Nos. 1-3 look as if they were growth-forms 

 of another qualitatively different type ; but 

 Dr. Emerson informs me that he has found 

 that the smaller forms (Sjostedt's Nos. 2 and 

 3) are both infested with an insect larva which 

 inhabits the head, and disproportionately 

 reduces its size ; these forms are not found 

 in nests from which the parasites are absent. 

 The differential retardation of the head might 

 be due to the existence of a true heterogony- 

 mechanism for the head, which is not nor- 

 mally manifested, but is revealed when the parasite produces 

 general size-reduction of the imago ; or it might be due merely 

 to the fact that the head is the seat of the infestation. 1 

 The difference between worker and soldier would appear 



1 In passing, we may note that the effects of such parasites may 

 be very striking ; e.g. in Termes gilvus, Silvester (1926) figures extra- 

 ordinary qualitative changes in shape of head and jaws, as well as a 

 general size-reduction and a highly disproportionate reduction in jaw- 

 size, as result of the presence of a similar parasite in the head. And 

 see, for a discussion of the corresponding problem in ants, Wheeler 

 (1928) and Vandel (1930). 



Fig. 38. — Heads of 

 largest and smallest 

 workers in a colony 

 of the termite Ter- 

 mopsis angusticollis, 

 showing heterogony 

 and change of pro- 

 portions with in- 

 crease of absolute 

 size. 



