HETEROGONY AND HORMONES 179 



the accessory organs relative to the gonad (see references in 

 Parkes, 1929, pp. 158-9). Thus it would seem that pre- 

 pituitary extract causes acceleration of the growth of the 

 gonad and accessory organs, but without inducing an increase 

 in the final maximum size of either, or a disproportionate 

 development of accessory organs relative to gonads ; while 

 injection of placenta-extract leaves the gonad of normal rela- 

 tive size, but apparently induces a supernormal production 

 of sex-hormone, this in turn resulting in supernormal hyper- 

 trophy of accessory sexual organs. We may expect to find 

 similar complications elsewhere as regards the relation of 

 hormone-producing organ and reactive organ. 



Champy (1924) has given us an interesting experiment on the 

 dorsal crest of male newts (Triton). This is a male secondary 

 sexual organ, appearing at the onset of the breeding season, 

 and exhibiting marked heterogony. Champy finds that it 

 shows a differential response to starvation, being reduced 

 relatively faster than other organs. 1 This may be due to the 

 crest consisting of material which is readily drawn upon in 

 starvation, or may point to some more general law of the 

 reversibility of heterogonic growth, according to which a 

 heterogonic organ would always tend to approach the size 

 appropriate to its partition-equilibrium whatever the bulk of 

 the body, and whether that bulk was being increased by normal 

 growth or reduced by starvation. That something of this 

 latter sort may occur is shown by the well-known fact that 

 planarian worms reduced in size by starvation revert to juvenile 

 proportions (Child, 1915). This relation has recently been 

 worked out quantitatively by Abeloos (1. c), who finds not 

 only that the change of proportions during normal growth is 

 truly heterogonic and approximates to that obtainable by 

 constant differential growth-ratio, but that it is almost exactly 

 quantitatively reversed during reduction due to starvation. 

 In any case, the example of Triton clearly demonstrates the 

 co-operation of nutritive and hormonic factors in determining 

 the size of an organ (Fig. 80). 



Non-sexual organs may, of course, also show heterogony, 

 and their heterogony may also depend upon hormones. This 

 is best seen as regards the growth of limbs in Anuran meta- 

 morphosis, which depends upon thyroid hormone, and is, up 



1 Unfortunately no weight-measurements of crest and other soft 

 parts were made ; but Champy's illustrations appear in general to 

 bear out his assertion. 



