EVOLUTION OF THE COLORS OF BIRDS. 5 



7. That gemmules are thrown off by all physiolog- 

 ical cells, not only during the adult state of the organ- 

 ism, but during all stages of development. Or, in other 

 words, that the production of these cell-seeds depends 

 upon the adult condition of parent cells; not upon that 

 of the multicellular organism." 



This theory has subsequently been varied in its details 

 by Brooks, Galton, Herdman, and others. According 

 to Brooks the ovary is passive and does not aid in the 

 transmission of acquired characters, but the sperm cells 

 contain gemmules which are thrown off from such parts 

 as are undergoing change. Galton believed to a con- 

 siderable degree in the continuity of the germ plasm, 

 although also holding that acquired characters are in- 

 heritable. For example, he says, " From the well- 

 known circumstance that an individual may transmit to 

 his descendents ancestral qualities which he does not 

 himself possess, we are assured that they could not have 

 been altogether destroyed in him, but must have main- 

 tained their existence in a latent form. Therefore each 

 individual may properly be considered as consisting of 

 two parts, one of which is latent and only known to us by 

 its effects on his posterity, while the other is patent, and 

 constitutes the person manifest to our senses."'" These 

 latent characters he considered to be transmitted from 

 generation to generation by means of a portion of the 

 gemmules of the fertilized ovum which remained unde- 

 veloped. Although at first adopting an hypothesis of 

 pangenesis he afterwards abandoned this for a theory of 

 the continuity of the germ-plasm not unlike that of 

 Weismann. 



Lloyd Morgan criticises the pangenetic hypothesis in 

 the following well chosen words: " The existence of 



'On Blood Eelationship, Pioc. Koy. Soc, 1872, p. 394. 



