OTHER THEORIES OF SPECIES-FORMING. 269 



nants," and of numerous other micromeric theories. 8 But 

 the facts of budding, especially as exemplified in plants, 

 and of regeneration among animals, both of these kinds of 

 phenomena seeming to show that germ-plasm is not neces- 

 sarily limited to the germ-cells, strictly so-called, have pre- 

 vented the acceptance of a too rigorous interpretation of 

 Weismann's distinction between the germ-plasm and the 

 soma, and have led to some theories of germ-plasm make-up 

 and disposition differing from the ones proposing a rigid 

 restriction of germ-plasm to the germ-cells. The facts that 

 in many plants any part, as a bit of a twig, say, if cut off, can 

 reproduce the whole plant just as effectively as a seed 

 (germ-cell) can, and that many animals can reproduce con- 

 siderable and complex parts, if lost by accident or self- 

 mutilation, show that there often resides in somatic cells of 

 much specialisation the capacity to reproduce not only cells 

 of their own kind but others of much variety and different 

 specialisation. So some biologists believe that there is either 

 a net-work of primitive germ-plasm extending throughout 

 the soma cells (Nageli's idioplasm theory for example), or 

 that each somatic cell (at least those with the capacity of 

 regeneration or reproduction by budding, cuttings, etc.) con- 

 tains a little primitive germ-plasm stuff besides its own 

 soma-plasm. And some authors have seen in such theories 

 of a widely diffused germ-plasm a mechanism for the trans- 

 mission from the soma to the central germ-cells of the 

 effects of use, disuse, and functional stimuli derived from 

 external sources. But does even this conception of a diffuse 

 and connected germ-plasm, after all, clear up in any way 

 our difficulty? It makes it easier to see how germ-plasm 

 may be affected by external and superficial influences, but 

 does it explain in any degree how these effects can be car- 

 ried to the germ-cells and so stamped on them as to compel 

 them to reproduce photographically in their later develop- 

 ment into new individuals, the specific effects that use, dis- 



