336 EVOLUTION AND ANIMAL LIFE. 



ventral fins are folded. When the action of the tail ceases 

 the pectorals and ventrals are spread out wide and" held at rest. 

 They are not used as true wings, but are held out firmly, acting 

 as parachutes, enabling the body to skim through the air. 

 When the fish begins to fall the tail touches the water. As 

 soon as it is in the water it begins its motion, and the body 

 with the pectorals again begins to vibrate. The fish may, by 

 skimming the water, regain motion once or twice, but it finally 

 falls into the water with a splash. While in the air it suggests 

 a large dragon fly. The motion is very swift, at first in a 

 straight line, but is later deflected in a curve, the direction 

 bearing little or no relation to that of the wind. When a 

 vessel passes through a school of these fishes, they spring up 

 before it, moAdng in all directions, as grasshoppers in a meadow. 



Among the insects, the possession of stings is not uncom- 

 mon. The wasps and bees are. familiar examples of stinging 

 insects, but many other kinds, less familiar, are similarly pro- 

 tected. All insects have their bodies covered with a coat of 

 armor, composed of a horny substance called chitin. In some 

 cases, this chitinous coat is very thick and serves to protect 

 them effectually. This is especially true of the beetles. Some 

 insects are inedible, and are conspicuously colored so as to 

 be readily recognized by insectivorous birds. The birds, 

 knowing by experience that these insects are ill-tasting, avoid 

 them. Others are effectively concealed from their enemies 

 by their close resemblance in color and marking to their 

 surroundings. These protective resemblances are discussed 

 in Chapter XIX. 



To the category of structures which may be useful in self- 

 defense belong the many peculiarities of coloration known as 

 "recognition marks.'' These are marks, not otherwise helpful, 

 which are supposed to enable members of any one species to 

 recognize its kind among the mass of animal life. To this 

 category belongs the black tip of the weasel's tail, which re- 

 mains the same whatever the changes in the outer fur. Another 

 example is seen in the white outer feathers of the tail of the 

 meadow lark as well as in certain sparrows and warblers. 

 The white on the skunk's back and tail may serve the same 

 purpose and also as a warning. It is apparently to the skunk's 

 advantage not to be hidden, for to be seen in the crowd of ani- 

 mals is to be avoided by them. That recognition is the actual 



