DOCTRINE OF EVOLUTION AND RELATED IDEAS 481 



the dog and the cow are also evidences of kinship ; and that their 

 differences mark a gradual evolution from a common stock in 

 special directions 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, 

 vestigial organs are also evidence of evolution of animals into 

 adjustment with the surroundings. 



486. Evidences from Embryology. The study of em- 

 bryology the course of life in the individual has probably 

 furnished us the most suggestive evidence of the evolution of 

 animals. The main facts, and the use that has been made of 

 them in reaching our conclusions, may be expressed in a few brief 

 statements. The student must go to more extended texts 

 for the complete handling of this complex but most interesting 

 subject. 



Some important facts of individual development are : 

 i. Each individual animal (with certain exceptions in 

 31 



