464 EVOLUTION, GENETICS, AND EUGENICS 



they ofiFer no difficulties because he can always fall back upon the 

 statement that, among the lower forms at least, there is reserve germ 

 plasm equally distributed over the whole body ready to differentiate 

 into definite germ cells when needed. This type of appeal is abhor- 

 rent to the physiologist, and with some justification, for it realh 

 begs the question by assuming that any cell that is capable of form- 

 ing germ cells belongs to the more or less sacred Uneage of germ plasm. 



If we confine the application of the germ-plasm idea to the higher 

 animals, such as vertebrates and insects, we would obviate these chief 

 objections, and the present writer would take the view that it is only 

 among the upper ranges of highly specialized animals that the con- 

 tinuity of the germ-plasm concept holds solidly. 



Another chief objection to the germ-plasm concept has to do with 

 '^ <=;upposed insulation or apartness of the germ plasm. Physiolo- 

 gists have found that there is an extremely intimate correlation in 

 function between practically all parts of a hving organism. Many 

 of the structures, such as the rudimentary pituitary body, the thyroids, 

 the adrenal body, and various other bodies whose function was long 

 unknown, have now been shown to exercise a profound effect on the 

 development of the whole body. Since practically all tissues are 

 known to affect at least some other tissues, is it hkely, the physiologist 

 asks, that none of the other tissues affect the germinal tissues ? The 

 organism is to be viewed, it is said, not as a collection of independently 

 functioning parts, but as a single coherent unit. On this view no 

 tissue can be thought of as beyond the influence of organic changes. 



The classic argument of the Weismannians was that we can con- 

 ceive of no mechanism by means of which somatic changes can be carried 

 back into the germ cells, and therefore there is no such mechanism. 

 Now the fallacy of this argument is obvious; even if we could con- 

 ceive of no suitable mechanism for this purpose, this does not preclude 

 the existence of such a mechanism. Moreover, according to Professor 

 Guyer, just such a mechanism actually exists, as will be brought out in 

 the following quotation from one of his recent publications. 



A POSSIBLE MECHANISM FOR THE TRANSMISSION OF 

 ACQUIRED CHARACTERS' 



MICHAEL F. GUYER 



Some selectionists ghbly assert that new characters arise as the 

 result of spontaneous changes in the germ. What is meant by this ? 



'From M. F. Guyer, "Immune Sera and Certain Biological Problems," 

 American Naturalist, Vol. LV (iq2i). 



