DOMESTICATED ANIMALS 47 



neys and two lungs. But in birds, for some rea- 

 son, the right ovary does nothing, and has shriv- 

 eled to a mere remnant. 



In man and most other vertebrate animals there 

 are two bones in the leg from the knee to the ankle 

 — the tibia and the fibula. In birds and in some 

 mammals there is but one bone (tibia), the fibula 

 being represented by a mere splint extending 

 down part v^^ay from the knee. You have prob- 

 ably seen this splint without recognizing it in the 

 leg of the chicken. The big bone in the chicken's 

 leg is the tibia ; the splint is the vestigial fibula. 



Insects ordinarily have two pairs of wings. But 

 flies have only one pair, the hind pair being repre- 

 sented by a couple of knobs. In other species of 

 insects the front wings are rudimentary. The 

 male cockroach has two pairs of wings, and occa- 

 sionally uses them in flying. But the female is 

 flightless, the wings being rudimentary. The ovar- 

 ies are vestigial in the working class of bees and 

 ants. In the cow there are two teats that are rudi- 

 mentary and four that produce milk. The rudi- 

 mentary teats occasionally yield milk. In one 

 breed of Chinese sheep the ears are mere vestiges, 

 and in another breed the tail has dwindled to ''a 

 little button smothered in fat." In tailless dogs 

 and cats there is a rudimentary stump. In some 

 breeds of chickens the comb and wattles are rudi- 

 mentary; and in the Cochin-China the spur has 

 nearly disappeared. In the hornless breeds of 

 sheep and cattle tiny knobs often grow out where 



