24 E VOL UTION AND DISEASE. 



same way that the hairy tuft may be accounted for in 

 the back of those with spina bifida occulta. These 

 fowls are extremely uncertain in their gait, given to 

 performing circular movements, and walking sideways if 

 excited, as though they possessed an unstable nervous 

 system. Darwin was assured that we had here to deal 

 with a character first acquired and transmitted by the 

 hen. 1 



FIG. 13. The head of a Polish fowl to show the feathery tuft. 

 (After Darwin.) 



A somewhat similar condition is seen in ducks. Pre- 

 served in the museum of the Royal College of Surgeons 

 is a duckling with a small tumour projecting from the 

 top of its head ; hanging from the side of the tumour is 

 a miniature but well-developed foot (fig. 14). The 

 swelling is connected with the duckling's brain by means 

 of a small rounded hole in the summit of the cranium, 



1 "Animals and Plants under Domestication." 



