188 PROBLEMS OF RELATIVE GROWTH 



There is one point in Hammett's discussion which needs 

 further consideration. He maintains that all the growth- 

 effects of thyroidectomy are what we may call non-specific, 

 due to its differential effects on different general kinds of 

 materials or metabolic activities. That this need not always 

 be so, however, is conclusively shown by the facts of Amphibian 

 metamorphosis ; in Anuran larvae thyroidectomy has a much 

 greater growth-retarding effect on the limbs than on any other 

 organ, in spite of the fact that the growth of these, normally 

 and under the effect of excess thyroid, is mainly due to cell- 

 multiplication (see above). There is, in fact, the possibility 

 of specific as well as of general differential effects of hormones 

 upon growth. 



This has been well brought out by Keith (1923), who has 

 pointed out that the pre-pituitary affects growth differentially, 

 acting most of all upon the extremities and on the parts con- 

 nected with jaw-function. And similar specific sensitivity is, 

 of course, abundantly shown in regard to the sex-hormones 

 (see above). Cushing (1912) points out that hyperpituitarism 

 is associated with relatively stout digits, hypopituitarism with 

 relatively slender ones. 



Although there are no sex-hormones in insects, reference 

 may be made here to Champy's interesting discussion (1929, 

 pp. 204 seqq.) of the relation between heterogony and secondary 

 sexual characters. In various genera of beetles, in which a 

 horn or other excrescence is normally present in males only, 

 it occurs in both sexes in certain species. When this is so, 

 the organ appears almost invariably to be highly heterogonic 

 when restricted to one sex, only slightly heterogonic or even 

 isogonic when present in both sexes (e.g. the beetle Phanaeus 

 lancifer as against other species of the genus). In Enema 

 infundibulum, and other beetles, the female possesses a cephalic 

 horn, but lacks a thoracic horn : in the male, the latter is 

 highly heterogonic, the former only slightly so. 



The same phenomenon is found as regards the ' tails ' of 

 the swallow-tail butterfly, Papilio dardanus. In the few sub- 

 species where the sexes are similar, the ' tail ' is isogonic ; 

 in the rest, it is heterogonic. He further states that the same 

 phenomenon occurs in Chameleons, Sheep, Antelopes, and 

 Deer (Reindeer, as against the other forms). Here, however, 

 quantitative data are lacking, and the statement needs 

 confirmation. 



Champy correctly stresses the frequent relation between 



