114 THE AMERICAN NATURALIST [Vol. LV 



change in the somatic element its germinal correlative 

 would presumably remain constant, but any alterations 

 of the soma which give rise to the formation of anti- 

 bodies or other active agents, particularly if long con- 

 tinued, might induce changes in the germ. Such a hy- 

 pothesis would seem to be plausible at least in account- 

 ing for degenerative changes such as the deterioration 

 of eyes in such forms as the mole, or in fact, in the for- 

 mation of vestigial organs in general. 



On the other hand, there is no reason to infer that 

 changes induced in the blood-serum may not also be in- 

 strumental in leading to progressive as well as regressive 

 evolution. If we may have germinally destructive con- 

 stituents engendered in the blood there is no valid reason 

 for supposing that we may not also have constructive 

 ones. When we learn more about what initiates and pro- 

 motes growth in a part through exercise, or what causes 

 hypertrophy of an organ, we may likewise find how cor- 

 responding germinal antecedents of that part may be 

 •enhanced. Until such time we shall probably remain in 

 the dark regarding the mechanism of progressive germ- 

 inal changes. As already indicated, in the hormones and 

 clialones we have a wonderful series of secretions nor- 

 iiially circulating in the blood and maintaining general 

 phy siological equilibrium. That reciprocal stimulations 

 of various organs occur by this means is a well-estab- 

 lished fact. Hypertrophy or atrophy of an endocrine 

 gland may produce pronounced effects in the further- 

 most reaches of the body. Again we may inquire, is it 

 reasonable to suppose that the germinal tissues will be 

 inviolate to all this ebb and flow of chemical influence? 

 SlidiiM we not oxpcct specific reactions or selections here 

 no Irv. -nroly tliaii in other tissues? Destruction of the 

 l):\v< liuccili- of the hypophysis in the frog-tadpole will 

 cau-i' profound alteration in other endocrine organs such 

 .'I- the ri«li eiials and thyroids, will retard the growth rate, 

 render tlie entire organism albinous, and produce in the 

 individual pigment cells a condition of sustained con- 



