368 THE BIOLOGY OF BIRDS 



the rest of the brain. The skull is transformed in correlation 

 with the change in the shape of the brain ; it is raised up in 

 the region of the frontal bones. Above this is the large 

 tuft of head feathers, and in connection with this hood the 

 blood-vessels of the head are quite peculiar. The comb is 

 much reduced in the hens, less so in the cocks ; below the 

 comb there are sometimes large vesicles containing serous 

 fluid. All the Houdans have five toes. In short, they are 

 bundles of abnormalities and they do not look happy after a 

 shower of rain. But the marvel is that under man's pro- 

 tection the Houdans fare not badly and have persisted for 

 many years. 



There seem to be conservative as well as variable types, 

 as may be illustrated by contrasting ostrich with pigeons or 

 poultry. Of distinct new departures in pigeons and poultry 

 we have given examples, but Professor J. E. Duerden, an 

 acknowledged expert on ostriches, writes (1919) as follows : 

 " Without any hesitancy it can be affirmed that in the course 

 of the fifty years during which the ostrich has been domesti- 

 cated, it has never produced a feather variation, germinal in 

 its origin, such as could be regarded as of the nature of a 

 sport or mutation. . . . The greatest mixture of germ-plasm 

 is going on, but no single hereditary factor or determiner is 

 altered in the process, and has not altered throughout the 

 history of ostrich breeding ; only new combinations are 

 formed of factors already available." Professor Duerden 

 allows that some degenerative phenomena are observable, 

 e.g. in the reduction of toe-scales, but he will not admit the 

 occurrence of anything positively new, with, perhaps, one 

 exception. 



The one new departure which Professor Duerden has 

 observed (191 8) is the occurrence of 42 plumes in the 

 first row of the wing. This was observed in two birds, 

 one of which survived and bred true. From a quantitative 

 variation of this sort it may be possible to raise a stock which 

 would give the same number of feathers from fewer birds. 

 The average number of plumes in the first row is 36*54 

 throughout Africa, the range being 33 to 39 ; the selection 



