THE GERM-PLASM 57 



sumption that each of the millions of cells in a multicellular 

 organism is represented in the germ-plasm by several or many 

 different kinds of biophors. There is, however, a simple and 

 natural way out of this dilemma, as soon as we inquire whether 

 every cell of a plant or an animal is independently variable at 

 all, and whether consequently it must be represented by special 

 elements in the germ-plasm. _ 



^hall desig nate the cells or groups of cells which are inde- 

 pendently variable from the germonwards as the • hereditary 

 parts^~m^^Jil£lei'JJiiiiai^^2iadi the particles of the germ-plasm 

 corresponding to and determining them, as the ' deterf/iitiiug 

 parts' or ' deter mittajits.' It is evident that many of the cells 

 in the higher animals are not represented individually in the 

 germ-plasm by a determinant. The millions of blood-corpuscles 

 which are formed during the life of a Vertebrate might possibly 

 be controlled in the germ-plasm by a single determinant. At 

 any rate no disadvantage to the species would result from this, 

 because the capacity for being independently determined on the 

 part of the individual blood-corpuscles, or even individual thou- 

 sands of them, would be of no value to the animal. They are 

 not localised : one of them has the same value as another, and 

 their variability therefore might well be controlled from a single" 

 point. In conformity with the law of economy. Nature would 

 not have incorporated more determinants than was necessary 

 into the germ-plasm. 



Thus there are probably many groups of cells in the higher 

 animals, the constituents of which are not represented individu- 

 ally in the germ-plasm. All the nerve-cells of the brain do. it 

 is true, possess their special determinants, as otherw-ise the trans- 

 mission of such fine shades of mental qualities in man would be 

 inexplicable ; but it can matter little whether each fibre of a 

 muscle, or each cell of the epidermis or of the epithelial lining 

 of the alimentary canal, has its special determinant : in the last- 

 mentioned cases larger or smaller ^/'^///j of cells are presumably 

 controlled by a single determinant. The manner in which the 

 epithelium of the alimentary canal is renewed amongst insects 

 may perhaps be taken as pointing to this assumption. In flies 

 and butterflies, for instance, as I have proved long ago, the 

 alimentary canal of the larva undergoes disintegration, and that 

 of the imago, which has a very different structure, is developed 

 out of its remains. Kowalewski and van Rees have since 



