344 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
facts learned from a study of precipitins and of anaphylaxis that each 
species of animal has a thread of fundamental similarity underlying 
the proteins of all its tissues. There is no reason to suppose that germi- 
nal tissue forms an exception. The further fact that homologous 
tissues, though existing in different species of animals, possess similar 
chemical characteristics, shows that to get an effect there need not 
be absolute chemical identity between the substance of such a tissue 
as the lens and the germinal constituents of which it is the expres- 
sion. And if this is true for lens, why not for other tissues ? 
The blood-serum of any organism with blood thus affords a means 
of conveying the effects of changes in a parental organ to the germ- 
cell which contains the antecedent of such an organ. As long as there 
is little change in the somatic element its germinal correlative would 
presumably remain constant, but any alternations of the soma which 
give rise to the formation of anti-bodies or other active agents, par- 
ticularly if long continued, might induce changes in the germ. Sucha 
hypothesis would seem to be plausible at least in accounting for 
degenerative changes such as the deterioration of eyes in such forms 
as the mole, or in fact, in the formation 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 instrumental in leading to pro- 
gressive as well as regressive evolution. If we may have germinally 
destructive constituents 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 promotes growth inapart 
through exercise, or what causes hypertrophy of an organ, we may 
likewise find how corresponding germinal antecedents of that part 
may be enhanced. Until such time we shall probably remain in the 
dark regarding the mechanism of progressive germinal changes. As 
already indicated, in the hormones and chalones we have a wonderful 
series of secretions normally circulating in the blood and maintaining 
general physiological equilibrium. That reciprocal stimulations of 
various organs occur by this means is a well-established fact. Hyper- 
trophy or atrophy of an endocrine gland may produce pronounced 
effects in the furthermost 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? Should we not expect 
specific reactions or selections here no less surely than in other tissues ? 
Destruction of the pars buccalis of the hypophysis in the frog-tadpole 
will cause profound alteration in other endocrine organs such as the 
