WEISM ANN'S THEORY OF THE GERMPLASM 81 



the reproductive-cells must be considered as much 

 a part of the organism as any other tissue. Some- 

 times they form the greater part of the body, as in 

 many parasites, and, like the other tissues, they 

 are subject to death, unless the conditions necessary 

 to their further development have occurred in 

 time. But under such conditions other cell-com- 

 plexes may have death averted from them, as, for 

 instance, when a slip cut from a willow-tree is 

 planted. Thirdly, the reproductive cells are 

 derived from the egg- cell just in the same way as 

 other tissue cells are derived from it. Like tissue 

 cells in multicellular organisms, they arise by the 

 specialisation of material separated from the egg- 

 cell, and, like every other organ, attain the position 

 assigned them in the plan of development in the 

 course of the general metamorphosis of position 

 that all the cells pass through. Often the sexual 

 cells, like those of other tissues, appear at a 

 distance of several cell-generations from the egg. 

 The intervening generations are specially numerous 

 in those animals and plants in which several sexless 

 generations come between the sexual generations 

 (e.g., many plants, coelenterates, worms, tunicates). 

 I cannot agree to the existence (in Weismann's 

 sense) of special germ-tracks. Naturally, I do not 

 deny that the sexual cells arise from the egg after 

 definite sequences of cell - divisions ; but this 

 happens in the case of all specialised cells, such as 

 muscle, liver, kidney, and bone cells. The con- 

 ception of special germ-tracks has no more sig- 

 nificance than there would be in the conception of 



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