136 APPLIED BIOLOGY 



shaped leaves would be considered another species. Other 

 points of structure, such as shape and color of seeds, size of 

 the plant, etc., enter into consideration; and so there are 

 known to be many species of each color of violet. 



All the species of violets taken together constitute the 

 genus Viola; and in giving the double names to species the 

 generic name Viola is followed by the names of the species, e.g., 

 Viola tricolor. 



Summarizing the above, we may define a species as a group 

 of closely similar individuals; and a genus as a group of 

 similar species. As an illustration of an animal genus and 

 species, we may take the dog genus, Canis, which includes 

 dogs, wolves, and jackals. We have no difficulty in recogniz- 

 ing dogs, because they have certain characteristics which 

 distinguish them from wolves and jackals. Hence all dogs 

 are included in the one species, familiaris. Likewise, wolves 

 differ from dogs and jackals, and so wolves are classed in 

 other species; and jackals in still other species. 



125. Families, Orders, and Classes. Genera (plural of 

 genus) are grouped into families. For example, fox, wolf, 

 dog, and other dog-like mammals are grouped together in the 

 dog family, Canidae. Similarly, cat, lion, tiger, leopard, 

 lynx, and many other cat-like animals, belonging to several 

 genera, are grouped together in the cat family, Felidse. The 

 marten, mink, otter, weasel, skunk, and badger belong to 

 a related family, the marten family. Then there is a bear 

 family, and a raccoon family. All the animals of the dog, cat, 

 marten, bear, and raccoon families have some general resem- 

 blances, particularly in that their structure is adapted to a 

 flesh diet, hence they are called the flesh-eaters or carni- 

 vores. Such an assemblage of similar families constitutes 

 an order. 



Another familiar order is that of the hoofed animals, such 

 as cow, horse, pig, sheep. Another is that of the gnawers or 

 rodents (rats, mice, squirrels, rabbits, gophers). Another 



