62 THE GERM-PLASM 



mentioned the olfactory setae of Gammarus, which are situated 

 individually on particular segments of the feeler. Each of these 

 can vary hereditarily, and thus it is necessary to assume special 

 determinants for them in the germ-plasm ; these, however, will 

 all be similar to one another. This is also true of the black 

 spots on the wings of certain butterflies, already referred to. In 

 LyccBua Argus, for instance, there is a spot on that part of the 

 wing which is known to entomologists as ' cell i b,' and this 

 spot is independently variable : it may be larger or smaller, and 

 the variations in it can be transmitted quite independently of 

 the numerous other black marks on the wing. The particular 

 spot referred to may have disappeared entirely in another species 

 of Lyccena^ while a precisely similar spot in ' cell 4 ' has become 

 much larger. We have also decided indications that homologous 

 parts in the two halves of the body in bilaterally symmetrical 

 animals can vary independently of one another. The human 

 birthmark mentioned above was always inherited on the left side, 

 and never on the right. 



If each detenninant occupies a fixed position in the germ- 

 plasm, // cannot have an indefinite or variable size and form, 

 but must form a complete unit by itself, from which nothing can 

 be removed, and to which nothing can be added. In other 

 words, we are led to the assumption of groups of determinants, 

 each of which represents a separate vital unit of the third degree, 

 since it is composed of determinants, which in their turn are 

 made up of biophors. These are the units which I formulated 

 on different lines long ago, and to which the name of ancestral 

 germ-plasms was then given. I shall now speak of them as 

 '■ids,''* a term which recalls the 'idioplasm'' of Nageli. 



I assume that just as the individual biophor has other quali- 

 ties than those of the determinant, which is composed of 

 biophors, so also does the id possess qualities differing from 

 those of its component determinants. The fundamental vital 

 properties — growth and multiplication by division — must how- 

 ever be attributed to the id as to all vital units. Several reasons. 



* I have already used this term in my essay on 'Amphimixis ' ('Amphi- 

 mixis, Oder die Vermischung der Individuen," Jena, 1891, p. 39). In my 

 earlier essays the ids were spoken of as ' ancestral germ-plasms,' the mean- 

 ing and derivation of which term will be explained in the chapter on 

 amphigonic heredity. 



