310 PERIPATUS, MYRIOPODS, AND INSECTS. 



with the serpents, and they swim with the fish." They beat 

 the elastic air with their wings, and though there cannot be 

 so much complexity of movement as in birds where the 

 individual feathers move, the insect wing is no rigid plate, 

 and its up and down motions are complex. They can soar 

 rapidly, but their lightness often makes horizontal steering 

 difficult. The wind often helps as well as hinders them ; 

 thus the insects which fly in and out of the windows of 

 express trains are probably in part sucked along. Marey 

 calculates the approximate number of wing strokes per 

 second at 330 for the fly, 240 for the humble bee, 190 for the 

 hive bee, no for the wasp, 28 for the dragon fly, 9 for a 

 butterfly. It has been found that for short distances a bee 

 can out-fly a pigeon. 



Skin. 



As in other Arthropods, the epidermis (or hypodermis) 

 of Insects forms a firm cuticle of chitin, which in the 

 exigencies of growth has sometimes to be moulted. This 

 cuticle is often finely marked, so that the animal seems 

 iridescent, and there are many different kinds of scales, 

 hairs, and spines. Chitin is not favourable to the develop- 

 ment of skin glands, but most insects have "salivary glands," 

 opening in or near the mouth, bees have wax-making glands 

 opening on the abdomen, aphides have " honey-dew " tubes, 

 not a few have poison bags, and many larvse besides silk- 

 worms have organs from which are exuded the threads of 

 which a cocoon is made. 



Muscular System. 



In very active animals like Insects, we of course find a 

 highly developed set of rapidly contracting striped muscles. 

 These work the wings, the legs, and the jaws. The result- 

 ing movements have this further significance that they help 

 in the respiratory interchange of gases, and in the circula- 

 tion of the blood. 



JVervoiis Syste//i. 



It is often remarked as marvellous that ants and bees, 

 with brains smaller than pin heads, should be so clever. 

 The more we know about an ant, " the more the wonder 

 grows, so small a head should carry all it knows," or seems 



