434 weismann's theory ob^ heredity. 



tliau aggregated packets of gemmules which have emauated from all 

 the cells of all the tissues of the organism. 



(4) That the development of a new organism out of the fusion of two 

 such packets of gemmules is due to a summation of all the develop- 

 ments of some of the gemmules which these two packets contain. 



(5) That a large proportional number of the gemmules in each packet, 

 however, fail to develop, and are then transmitted in a dormant state 

 to future generations, in any of which they may be developed subse- 

 quently, thus giving rise to the phenomena of reversion or atavism. 



(6) That in all cases the development of gemmules into the form of 

 their parent cell depends on their suitable union with other partially 

 developed gemmules, which precede them in the regular course of 

 growth. 



(7) That gemmnles are thrown ofl' by all physiological cells, not only 

 during the adult state of the organism, but during all stages of its de- 

 veloi)meut. Or in other words, that the production of these cell seeds 

 depends upon the adult condition of parent cells, not upon that of the 

 multi-cellular organism as a whole. 



At lirst sight it may well appear that we have here a very formidable 

 array of assumptions. But Mr. Darwin ably argues in favor of each of 

 them by pointing to well-known analogies, drawn from the vital proc- 

 esses of living cells, both in the protozoa and metazoa. For example, 

 it is already a well-recognized doctrine of physiology that^ach cell of a 

 metazocin, or multicellular organism, though to a large extent depend- 

 ent on others, is likewise to a certain extent independent or automatons, 

 and has the power of multiplying by self division. Therefore, as it is 

 certain that the sexual elements (and also buds of all descriptions) in 

 elude formative matter of some kind, the first assumption — or that 

 which supposes such formative matter to be inarticulate — is certainly 

 not a gratuitous assumption. Again, the second assumption — namely, 

 that this particulate and formative material is dispersed throughout all 

 the tissues of the organism — is sustained by the fact that both in cer- 

 tain plants and in certain invertebrate animals a severed portion of the 

 organism will develop into an entire organism similar to that from which 

 it was derived, as for example is the case with a leaf of begonia and 

 with portions cut from certain worms, sea-anemones, jelly-fish, etc. This 

 well-known fact in itself seems enough to prove that the formative ma- 

 terial in question must certainly admit (at all events in many cases) of 

 being distributed throughout all the tissues of living organisms. 



The third assumption — or that which supposes the formative mate- 

 rial to be especially aggregated in the sexual elements — is not so much 

 an assumption as a statement of obvious fact; while the fourth, fifth, 

 sixth, and seventh assumptions all follow deductiv'ely from their pred- 

 ecessors. In other words, if the first and second assumptions be 

 granted and if the theory is to comprise all the facts of heredity, then 

 the remaining five assumptions are bound to follow. 



