HOW ANIMALS ARE CLASSIFIED 19 



of animals may be compared to a tree whose largest 

 branches correspond to the phyla, the secondary branches 

 representing the classes, the branches of these the orders, 

 and so on, the leaves at the tips of the branches represent- 

 ing the species. 



As it is often desirable to determine the group to which a 

 particular animal belongs, guides to the proper group are 

 often given in the form of a key. In using the following 

 key to the families of the orthoptera ascertain first if the 

 insect falls under the group A. If not try AA. If it 

 goes in the latter division see whether it falls under B or 

 BB. If it comes under BE, then find whether it belongs 

 in C or CC. After finding the family, the genus and the 

 species to which the insect belongs may be determined in 

 a similar manner. As the genera and species of Orthop- 

 tera are so numerous, it is necessary to refer the students 

 to more advanced works for this infomation. 



Key to the Common Families of the Orthoptera 



A. Posterior legs larger than the others and fitted for leaping. 



B. Antennae much shorter than the body. Organ of hearing, when 

 present, on the base of the first abdominal segment 



Acridiidae, or short-horned grasshoppers. 



BB. Antennas longer than the body. Auditory organs generally in the 

 base of the tibia of the first pair of legs. Ovipositor generally 

 long. 



C. Tarsi four-jointed, ovipositor flattened Locustidae, or long- 

 horned grasshoppers. 



CC. Tarsi three-jointed. Ovipositor very slender and somewhat en- 

 larged at the tip Grillidae, or 



crickets. 



A A. Posterior legs not much longer than the others and fitted for 

 walking or running. 



B. Body rather short and broad, flattened; head partly inserted in the 

 broad prothorax Blattidae, or cock- 

 roaches. 



BB. Body elongated. 



C. Fore legs large, spiny, fitted for grasping prey, prothorax long. 

 Mantidae. 



CC. Fore legs not large, prothorax short Phasmidae. 



