THE GERM-PLASM THEOBY 



; 



of many insects. Many grasshoppers produce sounds by addline 



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

 anterior wing upon the other, and, indeed, always with one particula] 



vein in one upon a particular vein in the other. ( toe of I hi 



as the bow, the other as the string, of the violin, and the bo* 



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 resounding vibrations. My pupils, Dr. Petrunkewitech and 



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



arisen as modifications of the hairs which are scattered everywh* 



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



' stridulating-vein,' have they been 



modified 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 all proba- 



bility vary only en bloc, as, for (Stenobothrus j a), after Graber. 



j. n -it i £ i i i n femur, ft, tibia, to, tarsal joints. 



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



in Man, the hundreds of thousands or 



millions 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 cartil 



or a bone, and so on. In all these cases a single determinant, oral 



least a few in the germ-plasm, may be enough. But in numen »us cases 



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



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



theory. In unicellular organisms the determinants will control parts 



of cells, in multicellular organisms often whole cells and groups of 



cells. 



Perhaps an inference as to the nature of the determinants may 



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



cells may be supposed to have simpler determinant- than whole cells 



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



91 



Elind Leg 





