112 



THE GERM-CELLS 



chromatin in part degenerates, in part is transformed, so that all of 

 the descendants of these side-branches receive small reduced nuclei." ^ 

 It would be difficult to overestimate the importance of this dis- 

 covery ; for although it stands at present an almost isolated case, yet 

 it gives us, as I believe, the key to a true theory of differentiation 

 development,^ and may in the end prove the means of explaining 

 many phenomena that are now among the unsolved riddles of the cell. 



Pig, 56. — Primordial germ-cells in Cyclops. [HXCKER.] 

 A Young embryo, showing stem-cell (st). B. Tlie stem-cell has divided into two, giving 

 rise to the primordial germ-cell {g). C. Later stage, in section; the primordial germ-cell has 

 migrated into the interior and divided into two; two groups of chromosomes in each. 



Hacker ('95) has shown that the nuclear changes in the stem- 

 cells and primordial eggs of Cyclops show some analogy to those of 

 Ascari:;, though no casting out of chromatin occurs. The nuclei are 

 very large and rich in chromatin as compared with the somatic cells, 

 and the number of chromosomes, though not precisely determined, 

 is less than in the somatic cells (Fig. 56). Vom Rath, working 

 in the same direction, has found that in the salamander also the 

 number of chromosomes in the early progenitors of the germ-cells 



1 Boveri. '91, p. 437. 



- Cf. p. 321. 



