74 HEREDITY 



and their soluble poisons or toxins enter the blood- 

 stream, they will soon be brought into immediate 

 relation with the germ-plasm. Again, the body con- 

 tains many glands, such as the thyroid and supra- 

 renals, which produce '' internal secretions " that are 

 carried by the blood to every part of the body and to 

 the germ-plasm. Plainly, any doctrine of the in- 

 violability of the germ-plasm is utterly untenable. 

 Also — though this point is more intricate and de- 

 bateable — the reproductive glands are subject to 

 nervous influences. Nerves pass to them from the 

 spinal cord, and no limit can be set, in the present 

 state of our knowledge, to the nature or potency of 

 the nerve-impulses that may thus connect the germ- 

 plasm with any part of the body and, through it, with 

 the remoter environment. 



If, then, we accept Weismann's conception of the 

 germ-plasm, we are now in a position tentatively to 

 make certain a priori assertions as to the transmis- 

 sibility of acquired characters — that transmissibility 

 upon which Lamarck based his theory of organic 

 evolution and of which AVeismann denies the exist- 

 ence. We must beware of attaching too much 

 weight to a priori reasoning, which has led men 

 astray ever since they began to think ; but neverthe- 

 less we are entitled to note the inferences which may 

 be legitimately drawn from our premisses — whether 

 or no these premisses be accurate. Later we must 

 approach the matter from the side of observation 

 and a posteriori reasoning. 



But assuming the accuracy of our assumptions, we 

 may say that we can readily conceive of the trans- 

 missibility of certain acquired characters. For in- 



