ANIMAL CLASSIFICATION— TAXONOMY *M 



Both of these were given the same species name because they were first 

 reported in the Carolinas. Sometimes when one refers to a particular 

 genus over and over again in a scientific paper it is permissible to use 

 only the first letter of the genus after it has been written out in full in the 

 first appearance of the word. Thus, you may see T. Carolina for the box 

 turtle or R. pipiens for the leopard frog. 



The most important varieties of animals are sometimes called sub- 

 species, and they usually exist only because they are isolated by some sort 

 of barrier which prevents them from breeding with others in the same 

 species. The red-shouldered hawks, Buteo lineatus, are divided into at 

 least four subspecies in the United States. The largest race is the eastern 

 red-shouldered hawk which is found east of the Rocky Mountains and 

 north of the Gulf States. It is given the subspecies name of lineatus. 

 Thus, the complete name of this variety is Buteo lineatus lineatus. It is 

 separated from the slightly smaller and more reddish race west of the 

 Rocky Mountains, the western red-shouldered hawk, B. I. elegans. To 

 the southward, in Florida, north to South Carolina and along the Gulf 

 westward into east Texas is the Florida red-shouldered hawk, B. I. alleni. 

 This is a smaller and paler variety, apparently isolated from the more 

 northern race by climatic barriers. In the Florida everglades and on the 

 Keys is found the insular red-shouldered hawk, B. I. extimus, which is still 

 smaller and paler and which is separated from the Florida red-shouldered 

 hawk by climatic conditions. At some points where the ranges of these 

 birds overlap slightly, there is inbreeding and hawks are found which 

 cannot be clearly assigned to either of the two subspecies which have 

 mingled together. 



In domestic animals we can maintain varieties by a control of the 

 breeding so that only members of the same variety are allowed to breed 

 together. In this way we keep varieties pure. Our many pure breeds 

 (varieties) of dogs bear testimony to the success of controlled breeding. 

 It is easy to see what would happen without this restraint on breeding, 

 when we see the mixtures of mongrel dogs that roam the streets of our 

 cities. Each dog is a type unto itself with a pedigree which is likely to 

 include many varieties. 



Such mixing of different species does not occur for a number of rea- 

 sons. For one thing, there is no sexual attraction between members of 

 different species as a general rule. A male dog is not sexually excited 

 by contact with a female cat who is in the phase of the reproductive cycle 

 known as "heat." Hence, there is no mating between the two. Even if 

 there were mating there would be no offspring. It is possible to artificially 

 inject sperms from a dog into a female cat that is ready for breeding, but 

 the sperms will not unite with eggs. There is a difference in the two spe- 



