270 DARWINISM TO-DAY. 



use, and external stimuli may have had on specific soma 

 parts of the parent ? 



Indeed, Haacke 4 well points out that many or most cases 



of apparently direct working of extrinsic influences on the 



body are really indirect, in that these influences 



division' 8 ^ not actua % directly modify the structure, as 

 a blacksmith's hammer modifies the shape of a 

 piece of red-hot iron, or a seal shapes the drop of melted 

 wax, but that they do it indirectly as stimuli inducing chemi- 

 cal processes, nervous impulses, etc. The adaptive re- 

 arrangement of spongy tissue in broken and poorly reset 

 long bones, apparently a direct reaction, is really only in- 

 direct, occurring through complex chemical processes, i. e., 

 the bringing of special bone-forming materials to certain 

 places, etc. The outer influences are all stimuli, not actual 

 sufficient causes or manipulations. 



Haacke makes a proposal of much ingenuity, after a keen 

 and suggestive discussion of the inheritance of acquired 

 characters problem, to explain how such an inheritance may 

 be effected. It is based on the fact that no characters are 

 directly acquired ; that is, that any change is only the result 

 of some external stimulus and not of a directly and imme- 

 diately moulding cause, and that, therefore, in any phenom- 

 enon of stimulus and effect much more of the body substance 

 than that composing the exact part or region modified is 

 influenced. From this Haacke sees the possibility, even the 

 necessity, of a modification of the whole constitution, includ- 

 ing the germ-plasm (or perhaps the germ-plasm is modified 

 as a result of the modification of the whole constitution or 

 body in which the germ-plasm is being developed and 

 formed). Thus every acquirement of a new character or 

 change in an old one must or may affect the germ-plasm. 

 With regard to passive organs such as the chitin skeletal 

 parts of insects and crabs, Haacke points out that they are 

 only the product of active organs, i. e., the secreting skin- 



