182 THE BIOLOGY OF THE SEASONS 



potent ia." But Harvey had no way of accounting for the 

 wonderful primordium with which he started, at times he 

 was not even sure that it was entirely due to the parents. 

 " Neither the schools of physicians nor Aristotle's discerning 

 brain have disclosed the manner how the cock and its seed 

 doth mint and coine the chicken out of the egg." 



We now know this much clearly, that the primordium 

 owes its peculiar virtue to the fact that it is continuous 

 through unspecialised cell-lineage with the fertilised egg 

 from which the parent arose. There is a sense, as 

 Galton said, in which the child is as old as the parent, for 

 when the parent's body is developing with manifold differ- 

 entiation from the fertilised ovum, a residue of unaltered, 

 unspecialised germinal material is kept apart to form the 

 reproductive cells, one of which may become the starting- 

 point of a child. Similarly Weismann, generalising from 

 cases where the lineage is visibly demonstrable, maintains 

 that the germinal material (germ-plasm) which starts an 

 offspring owes its virtue to being materially continuous with 

 the germinal material from which the parent or parents 

 arose. Since Virchow's Cellular-Pathologie in 1858, there has 

 been a growing acceptance of this idea of germinal con- 

 tinuity, which makes development a little less of a puzzle. 

 There is a beadlike continuous lineage of germ-cells, of 

 which individuals are the mortal pendants ; the parent is as 

 much a trustee of the germ-plasm as the producer of the 

 child. In a new sense, the child is a chip of the old block. 



We do not know how the potentiality of a bird is con- 

 densed into a little clear drop of protoplasm with a nucleus 

 lying on the top of the yolk, just as we do not know how the 

 potentiality of doing very effective and wonderful things is 

 condensed into the pin-head brain of the exceedingly un- 

 teachable ant ; but we do know now how the germ-cell 

 differs from the cells of the body of the parent, being, through 



