132 Animal Life and Intellige^tce. 



freely throughout the body, but eventually find a home in 

 the reproductive cells. Just as the organism produces an 

 ovum from which an organism like itself develops, so do 

 the cells of the organism produce gemmules, which find 

 their way to the ovum and become the germs of similar 

 cells in the developing embryo. ** The child, strictly 

 speaking," says Darwin, " does not grow into a man, but 

 includes germs which slowly and successively become 

 developed and form the man." *'Each animal may be 

 compared with a bed of soil full of seeds, some of which 

 soon germinate, some lie dormant for a period, whilst 

 others perish.'* Or, to vary the analogy, "an organic 

 being is a microcosm — a little universe formed of a host 

 of self-propagating organisms." This is Darwin's pro- 

 visional hypothesis of pangenesis, which has recently been 

 accepted in a modified form by Professor W. K. Brooks in 

 America, to some extent by De Vries on the Continent, by 

 Professor Herdman of Liverpool, and by other biologists. 

 The ovum on this view is to be regarded as a composite 

 germ containing the germs of the cellular constituents of 

 the future organism. The scheme representing this view 

 will stand thus — 



^_____ — Skeletal and protective cells ,^ ^ sk. and pr. ^,,^ ^--^ s. 



Reproductive cell O Nerve and muscle cells -^Q^— n. and m. — ^Q '- n. 



"""----Glandular and nutritive cells ^''^ ^^ gl. and nu. -"^ ^~~^^ gl. 



It is clear that, on this hypothesis, we may frame an 

 apparently simple and, on first sight, satisfactory theory of 

 heredity. Since all the body-cells produce gemmules, 

 which collect in or give rise to the reproductive cells, and 

 since each gemmule is the germ of a similar cell, what can 

 be more natural than that the ovum, thus composed of 

 representative cell-germs, should develop into an organism 

 resembling the parent organism ? Modifications of structure 

 acquired during the life of the organism would thus be 

 transmitted from parent to offspring ; for the modified cells 

 of the parent would give rise to modified gemmules, which 

 would thus hand on the modification. The inheritance of 

 ancestral traits from grandparent or great-grandparent 

 might be accounted for by supposing that some of the 



