368 EVOLUTION, GENETICS, AND EUGENICS 



mammal warm-blooded. The internal anatomy of the three differs 

 fundamentally in every detail. 



A list of other types of convergence will more adequately illustrate 

 the law. 



Flying and parachuting animals occur among nearly all vertebratt 

 and some invertebrate classes. Planes of some sort are found for 

 supporting the body in the air. The plane is made in various ways 

 in different groups, but functions much the same in all of them. 



Running animals of various classes have long legs, and a tendency 

 to stand on the toes. There is also in several unrelated groups the 

 tendency to reduce the number of toes, the culmination of which is 

 seen in the one-toed horses. 



Climbing animals are all provided with clinging appendages of 

 some sort, including such structures as hooked claws, prehensile 

 fingers or tail, suction pads on the feet, and other similar adaptations. 



Burrowing animals have, as a rule, extra-heavy shoulder girdle 

 and strong fore limbs with heavy gouging claws. Many of them also 

 are blind or nearly so, as befits life in dark underground passages. 



Desert-dwelling animals as a rule are provided with heavy 

 scales, spines, or armor, to prevent excessive loss of moisture and as a 

 protection against spiny plants. They also usually have burrowing 

 habits enabling them to escape the extremes of heat and cold. 



Cave animals are usually blind or nearly so and are relatively 

 pale in color, sometimes without any pigmentation. 



Deep-sea animals of many sorts have phosphorescent organs by 

 means of which they either attract their prey or find their way about 

 the dark sea floor. Some of these organs, called "lanterns," can be 

 used as searchlights. The eyes of deep-sea fish are either enormously 

 large or are "telescope eyes," adapted for sensing light of low 

 intensities. 



Ant-eating animals, belonging to several distinct groups, are 

 heavily armored against the attacks of ants, have strong claws for 

 digging up ant galleries, have long snouts or beaks with a long sticky 

 tongue for capturing ants, and an arrangement of the glottis to prevent 

 ants from crawling into the lungs. 



2. There are almost innumerable examples of the law of divergence 

 of form, which is called also the law of adaptive radiation. Almost 

 every successful class or order of vertebrate animals, for example, 

 has members that have adjusted themselves to all of the main modes 

 of living. Thus among lizards, for example, there are primitive 



