DOCTRINE OF EVOLUTION AND RELATED IDEAS 487 



have many fundamental points in common. They are all warm- 

 blooded, covered with hair, have mammary glands, carry the 

 young in the uterus attached by a placenta. Hence they belong 

 to the subclass placentals and to the class of mammals. They 

 have similar parts to their skeletons, similar arrangements of 

 the principal muscles, similar structure of the brain and central 

 nervous system. Thus it might be shown that the Newfound- 

 land and the spaniel are similar to all the vertebrates, and 

 finally to all the animals. 



If the similarities of structure in a litter of kittens or in a 

 human family are a sign of kinship, we may equally believe that 

 the similarities between the dog and the cow are also evidences 

 of kinship ; and that their differences mark the result of a gradual 

 evolution from a common stock in special directions determined 

 by inheritance and in adjustment to special modes of life through 

 long ages of time. 



485. Evidences from Rudimentary Organs. — It often hap- 

 pens that some animals possess organs in only a slight or rudi- 

 mentary way, which in other animals are well developed and 

 useful. In the rabbit, for example, there is a pouch called the 

 caecum at the junction of the small and the large intestine. It. 

 is several inches in length, well supplied with glands, and proba- 

 bly of considerable value in digestion. In many mammals this 

 structure is much reduced, and in man it is only found as a 

 "vermiform appendix," which certainly has no such value as it 

 has in the rabbit, and is thought by many physiologists to be a 

 positive menace. 



Similarly, in many mammals there are certain muscles by 

 which the external ear is moved and directed so as to catch the 

 sound waves. In man these muscles, though present, are so 

 reduced as to be of no value. Most animals have many rudi- 

 mentary remnants of organs which are useful in other apparently 

 related animals. It is said that man alone has several hundred 

 such rudimentary structures. The rudimentary eyes of fishes 

 and Crustacea in caves, and the almost or entirely reduced organs 

 of many parasites are mute testimony of the loss of organs once 

 useful, through changed life conditions. In other words, 



