PERSISTENCE OF THE GERM-PLASM 449 



branes, tracheae, glandular cells, scales, pigment deposits, and 

 pointed tail, arises through the successive interposition of numer- 

 ous determinants in the course of cell-multiplication." 



In any case, whether the idea of representative primary 

 constituents commends itself to us or not, we must remember 

 that it is a fact that the organism — unified as it is — is built 

 up of a very large number of independently variable, inde- 

 pendently heritable items. 



The Persistence of the Germ-plasm. — We have given an 

 outline of the consistently- thought-out scheme which Weismann 

 has suggested as an interpretation of development — the dis- 

 tribution of the determinants, their " maturation," their " libera- 

 tion," their migration from the nucleus, their dissolution into 

 biophors, and the manner in which the biophors may control 

 the area or cell in which they find themselves. But it remains 

 to inquire how the germ-cells which start the next generation 

 are constituted. If the building-up of the body involves segre- 

 gation of the determinant architecture into smaller and smaller 

 groups, how does the organism produce germ-cells — that is, cells 

 with intact germ-plasm — with a complete equipment of deter- 

 minants ? The answer, already given in Chapter II., is that 

 it does not in the strict sense produce them ; they are there 

 all the time. 



In more detail, Weismann's answer (1885) — the theory of the 

 continuity of the germ-plasm — is that in the divisions of the 

 ovum the whole of the germ-plasm is not broken up into deter- 

 minant groups ; part of it is kept intact and handed on from cell 

 to cell along a lineage or " germ-track," which may be very 

 short or very long, until, sooner or later, it stamps a cell as a 

 primordial germ-cell. In other words, while most of the cells, 

 derived by division from the fertilised ovum become differenti- 

 j ated as body-cells, some of the cells retain a quota of intact 

 germ-plasm, and eventually give rise to recognisable germ-cells. 

 Body-cells and reproductive cells alike owe their being to the 



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