60 PROBLEMS OF RELATIVE GROWTH 



There is a further point to consider in regard to heterogony 

 in holometabolous forms. In other organisms — a fiddler-crab, 

 for example — the growing system is an open one, in that it 

 is continuously taking in food as it grows. The beetle or 

 other holometabolous insect, however, during most of the 

 period when the form of its adult organs is being laid down, 

 is a closed system, taking in no further food, but depending 

 on accumulated reserves and on the material derived from 

 the breaking down of larval organs. This has two conse- 

 quences for our problem. In the first place, in other forms 

 the fairest comparison of relative size would seem to be between 

 heterogonic organ and rest-of-body, since the size of the 

 ingestive and digestive systems are functions of the size of 

 the rest of the body, not of total size, as may easily be realized 

 by reference to the fiddler-crab. Here two large specimens, 

 male and female respectively, of equal rest-of-body weight 

 and therefore presumably equal-sized alimentary systems, will 

 be of very different total weight, since in the female either 

 chela will weigh only 2 per cent, of the rest-of-body, while in 

 the male the large chela may weigh up to 70 per cent, or more. 

 But in a stag-beetle, for example, the conditions are quite 

 different. Larvae of both sexes have jaws and guts of the 

 same relative size. A male and a female larva of the same 

 total size will have the same amount of reserve material, but 

 during the pre-pupal and pupal period, say 1 per cent, of 

 this is converted into imaginal female mandible, while perhaps 

 10 or 15 per cent, has to be converted into imaginal male 

 mandible. Since the amount of reserve material is here the 

 important factor for growth, it is total bulk, and not rest-of- 

 body bulk, which should be here used as the standard against 

 which to plot the bulk of the heterogonic organ (see Huxley, 

 1931c). 



This is a minor methodological point ; but it has further 

 consequences. To continue the example of stag-beetles, we 

 should accordingly expect, in an exceptionally large male 

 specimen where the theoretical relative size of the mandibles 

 would be huge (as long as the rest of the body in some speci- 

 mens of Cyclommatus tarandus : Dudich, 1923 ; see Fig. 91), that 

 during the longer time necessary to lay down this large organ, 

 the limited reserve-supply would come to an end, used up by 

 other competing organs, and therefore that the organ would 

 fall below the theoretical size expected on the formula for a 

 constant coefficient of growth-partition. Thus, owing to the 



