THE FORMATION OF GERM-CELI,S I9I 



form one nucleus. And, strictly speaking, even this assumption 

 would be by no means sufficient, for it does not account for the 

 architecture of the germ-plasm : the material only would be 

 provided. Such a complex structure can obviously only arise 

 historically. 



The fact that somatic idioplasm cannot again give rise to 

 germ-plasm serves as an additional support for the theory of the 

 germ-plasm as here developed. Invisible, or at any rate un- 

 recognisable, masses of unalterable germ-plasm must have been 

 contained in the body-cells in all cases in which such a trans- 

 formation has apparently occurred. 



These masses need not necessarily be invisible, for they can- 

 not be smaller than ids ; and if it should subsequently be proved 

 that the microsomes of the nuclear rods do actually correspond 

 to ids, we may hope to ascertain the exact number of these ids 

 in the individual species. An extensive field would then be 

 opened out for further investigation, for it would be possible to 

 decide by direct investigation whether the cell-series of the 

 germ-tracks carry along with them a larger or a smaller number 

 of ids than is contained in the fertilised egg-cell, and also the 

 relative proportion of the number of ids in the somatic cells in 

 the germ-track. We may thus hope that facts will come to light 

 which can be utilised in connection with this theory. 



Observations of this kind have already been made which indi- 

 cate an actual continuity of the germ-plasm. Boveri * observed 

 that the differentiation of the somatic cells from the primary 

 sexual cell in the segmenting egg of Ascaris niet^alocepJiala is 

 accompanied by a peculiar diversity in the nuclear structure. 

 The nuclei of the somatic cells throw off a large part of their 

 chromatin, in which process each idant loses a similar amount 

 of .substance. Further facts and illustrations of the process are 

 stil! wanting, but even did we possess them it would be neces- 

 -sary to postpone the detailed theoretical explanation of such 

 observations until we were able to judge as to the universal 

 occurrence of the process. Observations which my assistant. 

 Dr. V. Hacker,f has made on the segmenting ovum of a crus- 



* Theodor Boveri, 'Anatom. Anzeiger II. Jahrgang,' No. 22, 1887; and 

 ' Zellen-Studien,' Heft 3, Jena, 1890, p. 70. 



t Valentin Hacker, Zool. Jahrbucher, Abth. f. Anat. und Ontog., Bd. v., 

 1892; and Archiv. f. mik. Anaf., Bd. 40, 1892. 



