THE GERM-PL.ASM 89 



The number of wing- and tail-quills is nevertheless definitely 

 fixed for every species of bird, and each of these feathers pos- 

 sesses a definite form, size, and coloration. We must assume 

 that viore than o)ie determinant is necessary for an entire 

 feather, for a feather is formed from thousands of epidermic 

 cells, which are not by any means all similar to one another, 

 either as regards form, mode of combination, or colour. Many 

 feathers are striped, while others have a brilliant ornamental 

 spot at the tip ; as in the case, for instance, of the peacock, 

 many humming-birds, and certain birds of paradise. The cells 

 to which these stripes and spots owe their origin, must contain 

 determinants which differ from those of the rest of the cells 

 which take part in the construction of the feather. We must 

 therefore conclude that at least one^ and often several, determi- 

 nants of the germ exist for each of these two kinds of cells ; for, 

 as is well known, ornamental spots of this kind are often formed 

 of several colours, and are very complex. 



It would be erroneous to suppose that the contour-feathers are 

 not determined individually in such birds as the raven, in which 

 the plumage is all of one colour ; but in such cases the qualita- 

 tive differences refer less to colour than to form and size. The 

 fact that each part of the feather is determined hereditarily, 

 even as regards its colour, is proved by the variation which 

 occurs, and which in individual species has resulted in certain 

 feathers being partially or entirely white, or being brilliantly 

 coloured, as in the case of the bird of paradise, which is allied 

 to the raven. One need only look through a collection of 

 humming-birds, and compare the females, which are so often 

 plainly coloured, with the wonderfully variegated males, in order 

 to become convinced that almost every contour-feather can vary 

 in almost any direction as regards coloration, form, size, and 

 minute structure. 



As has already been remarked, the internal organs are ap- 

 parently by no means so specially determined from the germ 

 onwards as are the external parts : their determinants must 

 therefore control larger regions of cells, as in the case, e.g., of 

 blood-corpuscles and epithelial cells. The number of deter- 

 minants in the germ-plasm of the higher animals is nevertheless 

 an enormous one, and it might certainly be doubted whether 

 such a large number of biophors as must be required for the 

 construction of an id of the germ-plasm could be contained 

 within a single id. 



