THE ANIMAL CLIMAX-THE CHORDATES 



345 



certain periods of the day when grazing 

 would be less dangerous and then retire 

 to secluded spots to finish the job of chew- 

 ing. The teeth of both the odd- and even- 

 toed animals are well adapted for cropping 

 grass and grinding it to the proper con- 

 sistency for digestion. 



The boy who attends the circus is forever 

 in awe of the slow moving, thick-skinned 

 elephant ( Proboscidea ) with its nose, in 

 the form of a proboscis or trunk, touching 

 the ground ( Fig. 13-64 ) . This handy organ 

 is responsible for the unusually short neck 

 of the elephant because it performs the 

 function of securing its grassy diet from the 

 ground or any other place it may be found. 

 It is also useful in obtaining water. Actu- 

 ally, it is a prolongation of the upper lip 

 including the nostrils, a structure which has 

 become highly muscular and very power- 

 ful. The teeth have undergone several 

 changes, the most striking of which is the 

 formation of the great tusks, which are 

 over-developed incisor teeth and, inciden- 

 tally, excellent weapons for offense. These 

 tusks are sought by the hunter because 

 there is a good market for ivory. 



There have been many elephants in the 

 past which were known as mammoths and 

 mastodons and which apparently have only 

 recently died out ( 15,000 years ago ) ( Fig. 



Fig. 13-64. The Indian elephant (E/ep/ios indica) with 

 its upper lip and nose drown out into a trunk, a 

 remarkable prehensile organ. 



Fig. 13-65. Two rodents that have become popular lab- 

 oratory animals. The white rat (top), a domesticated 

 variety of the Norway rat (Roffos norvegicos) and 

 the guinea pig, a domesticated variety of the South 

 American cavia (Covia porcellus). 



25-2 ) . In Siberia, within the past few years, 

 mammoths have been taken from glacier 

 ice in which they were completely pre- 

 served, skin, flesh, and all. Such bodies have 

 been found partially eaten by wolves, and 

 in some cases man has fed upon these 

 ancient remains. 



Some relatives of the elephants went into 

 the sea and became adapted for an aquatic 

 existence. These are the Sirenia, which in- 

 clude such mammals as the dugong of the 

 Indian Ocean, the sea cows formerly from 

 Bering Straits but now practically extinct, 

 and the manatee from the Atlantic Ocean 

 in the tropics. These ugly, stupid beasts 

 feed on the abundant marine vegetation 

 along the shores but are unable to come 

 ashore themselves because they lack pos- 

 terior appendages and the front ones are 

 adapted for swimming only. The Sirenia 

 are not related to the whales; fossil records 

 indicate that their closest relatives seem 

 to be the Proboscidea, in spite of the vast 

 difference in their external appearance and 

 way of life. 



The most successful of all the mammals 

 are the rodents ( Rodentia ) , the "gnawers." 

 These include many small mammals com- 

 monly known to everyone: squirrels, chip- 



