A COMMENTARY ON LAMARCKISM 



anism which determines the differences between the zygotes of 

 higher organisms, and the cytoplasmic system, in a highly 

 regimented form, persists in the mechanism which gives rise to 

 differences between the cells that descend by mitotic division 

 from the zygote. In other words, cytoplasmic and nuclear 

 systems of inheritance live side by side in micro-organisms 

 because heredity and development have not yet sorted them- 

 selves apart; a lineage of protozoans has something in common 

 both with a lineage of higher organisms and with the lineage 

 of cells which arises from the zygote of each one. It may there- 

 fore be, as Sonneborn has long insisted, that in studying the 

 cytoplasmic hereditary mechanisms of protozoa one is attack- 

 ing not indeed the problem of embryonic differentiation itself 

 but the first and perhaps most vulnerable outpost of its 

 remarkably stubborn defences. 



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p. 58. 

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Beer, G. R. de (1951). Embryos and ancestors. 2nd Ed., Oxford. 

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