fe) EVOLUTION AND DISEASE. 
indeed we are fully justified in stating that this nasal 
horn of the rhinoceros is a gigantic wart (fig. 5). Pro- 
fessor Flower recently exhibited at the Zoological 
Society the skin from the head of a rhinoceros shot 
in Central Africa with three nasal horns. The accessory 
one measured twelve centimetres in height and more than 
forty-two in circumference. It 
was situated in the same line 
posteriorly to the normal horns. 
It was structurally a wart. That 
cutaneous horns should arise in 
oxen and other hollow-horned 
ruminants (Cavzcornza) need not 
surprise us when we reflect that 
the corneous caps of their natural 
horns are modified portions of 
the integument. 
Birds not infrequently exhibit 
wart-horns of this character, and 
an example growing from the leg 
of an oyster-catcher is shown in 
fig. 6. Such horns, whenever 
Fic. 6.—The leg of an Oyster 
Catcher (Hamatopus ostra- they have been observed in birds, 
Zegus) with alargewarthom. foliow the usual course of avian 
dermal organs in general, and are shed with each 
moult and reproduced with the new feathers. The 
horn on the leg of the oyster-catcher when compared 
with the size of the bird is very large. It is represented 
one-fourth its natural size. 
The shedding of pathological cutaneous horns and 
their subsequent reproduction has more than one 
