The Evidence from Variation. 159 



Tropical sheep with long coarse hair usually have 

 gout-like horns. Inherited baldness in man is often 

 accompanied by deficient teeth, and the renewal of the 

 hair in old age by a renewal of the teeth. The famous 

 hairy Burmese had deficient teeth, and both peculiarities 

 were hereditary. A Spanish dancer, Julia Pastrana, had 

 a full beara and a double set of teeth, and the daily papers 

 have recently contained an account of a man, living near 

 Lebanon, Pennsylvania, with no hair, teeth, or sweat 

 glands. 



The homologous parts of plants often vary in the 

 same way, as is well shown by certain compound flowers, 

 in which the stamens and pistils closely resemble petals. 



According to our view of the cause of variation we can 

 easily see how gemmules from a cell in one hand might 

 hybridize, and thus cause variation in the correspond- 

 ing cells of all four extremities, or perhaps in the em- 

 bryonic cell from which all these cells are derived, for in 

 the same way that an animal can unite sexually either 

 with another of its own race or with one which is some- 

 what less closely related to it, so I assume that a gem- 

 mule may unite with the particle of the ovum which cor- 

 responds to it, or with some other closely related par- 

 ticle. For example, agemmule which is thrown off from 

 a particular epithelial cell may simply cause modification 

 in the corresponding cell of the offspring, or it may 

 cause modification in a cell which is to produce this par- 

 ticular cell and a number of others. 



If each variation is purely fortuitous the- number of 

 generations which would be necessary in order to convert 

 a species with black hair into a spscies with every hair 

 brown or with every hair red is almost inconceivable, 

 but this difficulty entirely disappears as soon as we rec- 

 ognize that gemmules from one part of the parent may 



