THE GEEM-PLASM THEORY 



371 



of many insects. Many grasshoppers produce sounds by fiddling 

 with the thigh of the hind leg on the wing, others by rubbing one 

 antei-ior wing upon the other, and, indeed, always with one particvdar 

 vein in one upon a particular vein in the other. One of these serves 

 as the bow. the other as the string, of the violin, and the bow is 

 furnished with teeth (Fig. 91), ranged beside each other in a long 

 row, which have the same function as the colophonium of the violin, 

 that is, to grasp and release the strings alternately, and thus to 

 produce re-sounding vibrations. My pupiLs, Dr. Petrunkewitsch and 

 Dr. Georg von Guaita, have recently proved that these teeth have 

 arisen as modifications of the hairs which are scattered everywhere 



over the wing and leg. But only in this one place, on the so-called 



' stridulating-vein,' have they been 



motlified to form stridulating teeth 



(schr). Thus this vein must be 



capable of transmissible variation by 



itself alone, that is, there must be 



parts contained in the germ-plasm, 



the variation of which causes a 



variation solely of this individual 



vein and its hairs, possibly even 



a variation only on certain hairs on 



this vein. 



On the other hand, there are 



also large regions, whole cell-masses 



of the body, which in aU proba- j.^^ ^^ H^^^ leg ^f a Locustid 



bilitv varv only en bloc, as, for (Sfeii<*o«irusj)ro(orma), after Graber. fe, 

 •' •' "^ £ i_i J 11 femur, ft. tibia, fa, tarsal joints, schr, 



instance, the milliards of blood-cells the stridulating ridge. 

 in Man, the hundreds of thousands or 



milhons of cells in the liver and other glandular organs, the thousands 

 of fibres of a muscle, or of the sinews or fascia, the cells of a cartilage 

 or a 1x)ne, and so on. In aU these cases a single determinant, or at 

 least a few in the germ-plasm, may be enough. But in numerous cases 

 it is impossible to say how large the region is which is controUed by 

 a single determinant, and it is, of course, of no importance to the 

 theorj-. In unicellular organisms the determinants will control parts 

 of ceks, in multiceUular organisms often whole cells and groups of 



ceEs. 



Perhaps an inference as to the nature of the determmants may 

 be drawn from this with some probability, m as far as mere parts of 

 cells may be supposed to have simpler determinants than whole cells 

 and groups of cells. The determinants in the chromosomes of um- 



