182 



ANIMALS WITH JOINTED LEGS— THE ARTHROPODS 



of the vertebrates in success as a group, although they have followed a 

 different pattern of development. 



Because of their great numbers and wide distribution, it is evident 

 that this group of animals is of considerable economic importance to 

 man. They are probably more important than any other phylum. On 

 the harmful side, they are serious competitors for our food supply ; we 

 must constantly fight some of them in order to secure the food for our- 



Courtesy General Biological Supply House 



Fig. 13.1. A brine shrimp from the Great Salt Lake. Although this lake contains 

 salt in a concentration of about 27 per cent, this little shrimp has adapted itself to live 



in this extreme environment. 



selves. They spread serious diseases which cause untold human suffer- 

 ing and death and make some parts of the earth uninhabitable by civi- 

 lized races of man. Many of them have bites and stings that are un- 

 pleasant, to say the least, and, in some cases, serious. On the beneficial 

 side, they provide us with quantities of food, medicine, clothing, and 

 chemicals ; they kill many of our enemies, including some in their own 

 group ; and they cross-pollinate many of our important plants. Thus, 

 while we have a difficult time getting along with the arthropods, we 

 would also have a hard time trying to get along without them. 



