THE GERM-PLASM THEORY . |«» 



I shall now call the hereditary substance of a cell its ■ idioplasm,' 

 after Nageli's example, although he sought it in the cell-substam 

 not in the nucleus, and had a different theoretical conception of its 

 mode of action. It was he, however, who conceived and established 

 the idea of the idioplasm as the bearer of the primary constituents, 

 an Anlagensubstanz, determining the whole structure of the organism 

 in contrast to the general nutritive protoplasm. Every cell contains 

 idioplasm, since every cell-nucleus contains chromatin, but I call 

 the idioplasm of the germ-cells germ-plasm, or the primary-con- 

 stituent-substance of the whole organism, and the cdmplexea of 

 primary constituents necessary to the production of a complete indi- 

 vidual — whose presence we have just shown to be theoretically 

 necessary — I csllids. In many cases these 'ids' might be synonymous 

 with chromosomes, at least in all the cases in which the chromosomi 

 are simple, that is, are not composed of several similarly formed 

 structures. Thus in the salt-water Crustacean, Artemia salina, 

 which possesses 168 minute granular chromosomes, each of th< 

 chromosomes must be regarded as an id, for each can in certain 

 circumstances be thrown out from the ovum by the reducing division, 

 or it can be brought into the most various combinations with 

 other chromosomes by fertilization. Each of them must therefore 

 consist of perfect germ-plasm in the sense that all the parts of an 

 individual are virtually contained in it; each is a biological unity, 

 an id. But when we see in many animals larger band-shaped or 

 rod-shaped 'chromosomes,' and when these are composed of a Beries 

 of granules, as they are, for instance, in the often mentioned Ascai 

 megalocephala, each of these granules is to be regarded as an id. 

 In point of fact, we find, instead of the two or four large rod-shaped 

 chromosomes of Ascaris megalocephala, a larger number of smaller 

 spherical chromosomes in other species of Ascaris. 



Compound chromosomes consisting of several ids, such as all 

 rod or band-like elements of the nuclear substance probably ai 

 I designate 'idants.' That they are composed of several individual 

 ids is not always clearly apparent because of the smallness of the 

 object, and even in larger ones this may only be seen in certain 

 stages. Thus we have in Fig. 88, A and B, two ' mother-sperm-cells ' 

 of the salamander; A at an earlier stage, in which the individual ids 

 are not visible; B at a later stage, in which the band has split> and 

 the rosary-like structure has become at once apparent. It is noi 

 possible, then, to see at once whether each chromosome corresponds 

 to one or to several ids. A more exact investigation of the processes 

 of reducing division has shown that there are chromosomes of simple 



