436 THE RESULTS OF EVOLUTION 



while at the bottom of the urn or pitcher is a fluid con- 

 taining a digestive enzym. If an insect, attracted by 

 the nectar, attempts to crawl into the urn it slips on the 

 smooth zone, falls into the liquid, and unable to escape 

 by reason of the hairs, it drowns, is digested and absorbed. 

 The Venus fiy-trap of the southeastern part of the United 

 States is another of these remarkable insect-trapping 

 species. The terminal portion of each of its leaves is 

 developed into two flat, highly sensitive lobes with numer- 

 ous hairs located around their margins. When an insect 

 settles upon this portion of the leaf the lobes close 

 like the jaws of a steel trap and the captive is digested. 

 This operation over, the lobes again open and the process 

 is repeated. 



This curious habit of ensnaring and digesting insects is 

 common to several other species occurring in this and 

 other countries. The interested student will find the sub- 

 ject entertainingly discussed in Darwin's " Insectivorous 

 Plants." 



Adaptations for Self-Defense. — Animals when in 

 danger of attack take flight and escape by virtue of fleet- 

 ness or the ability to hide, or they may defend themselves 

 by means of claws, horns, teeth, and various other organs. 

 The rabbit, for example, when in danger, dashes into its 

 burrow, various species of birds escape into thick vegeta- 

 tion, certain fishes bury themselves in the mud, while 

 hosts of insects, spiders, and crabs conceal themselves 

 under sticks and stones and in other safe retreats. There 

 are also many species whose protective covering renders 

 them comparatively free from attack. The spines of 

 many crabs, fishes, porcupines, the armor of the arma- 

 dillo, the shells of clams and snails, are familiar examples 

 of this. In several species an additional protection 

 is afforded by poison, which in some of the sea urchins 

 and fishes is situated in small cavities in or near the 

 spines. Poison sacs are also a characteristic feature of 

 many snakes, all of the spiders, centipedes, the stings of 



