194 READINGS IN 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 vertebrate 
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 
