Weismann's Ancillary Hypothesis 55 



to accept the ancillary hypothesis must also give up the 

 principle of the uniformity of the germ-plasm. 



Weismann has connected his theory in a clear way 

 with the results of cell-study. He assumes that the nucleus 

 dominates and determines the nature of its cell, and also 

 that, for all functions of the cell, the material bearers of 

 the hereditary characters must be situated in the nucleus. 

 He assumes further that these bearers are arranged in 

 rows on the chromatin-thread of the nucleus, and points 

 out how, with this assumption, all the hereditary char- 

 acters are divided through the longitudinal splitting of 

 the nuclear skein, and how they are distributed among the 

 two daughter-cells. 



On the basis of these and similar conceptions, he also 

 treats the question concerning the cause of the differences 

 between the single organs of an individual. It is clear 

 that this question forms a great difficulty of the theory. 

 For the assumption of the ancestral plasms, every one of 

 which represents all the characters of the individual, can, 

 of itself, not serve as an answer, especially in connection 

 with the thesis just mentioned, that the nature of the 

 nucleus determines the character of its cell. 



Let us see what ancillary hypothesis Weismann uses. 

 The theory of heredity demands that, on the germ- 

 tracks,"^ the completeness of the germ-plasm be preserved, 

 for every egg-cell and every bud contain, on the whole, 

 the same hereditary elements as the germ-cells of the pre- 

 vious generation. In all the sequences of generations of 

 cells, which lead from one egg-cell to the germ-cells that 

 come next in order, (and these are the germ-tracks), the 

 germ-plasm must therefore remain the same. In all other 

 cells, however, which do not belong to the organs capable 



23Cf. Part II, A. p. 79. 



