422 GENERAL ZOOLOGY 



the summer, and going far to sea in the winter. The males 

 do not reach their full size and strength till about the seventh 

 year, and until that age the young males herd by themselves, 

 being forbidden the general herd by the older males. The 

 females mature in two years. Early in May the full-grown 

 males appear at the islands, and the females a few weeks after- 

 ward. Each male immediately collects as many females as 

 he can guard, and battles are frequent before the groups are 

 made up. The old males begin to leave the beaches about 

 the middle of July. Seal-hunters are restricted in their oper- 

 ations to killing the young males of three years of age 

 and upwards. This restriction tends to prevent the extermi- 

 nation of the species. The fur is most valuable between the 

 ages of three and seven years. 



Insect-Eating Mammals. The insect-eating mammals, Insec- 

 tiv'ora, are usually of small size. The teeth are sharp and 

 numerous, and the molars have sharp points for crushing the 

 bodies of insects. The eyes are often small and hidden in 

 the fur, especially in the forms which, like the moles and 

 shrews, burrow in the ground. The star-nosed mole (Con- 

 dylu'ra crista'ta) is a common American species living in 

 peat-swamps and rich land near ponds and streams. They 

 make great burrows, and the earth thrown up may sometimes 

 make a pile a foot or more in diameter. The name is given 

 from a fleshy filamentous appendage on the nostrils, which 

 is probably used as an organ of touch. Some of the shrews 

 are the smallest mammals known. They generally live in 

 burrows like the moles. They somewhat resemble mice, from 

 which they can be distinguished by the different plan of 

 the teeth. 



Bats. The Chirop'tera (Gr. cheir, hand ; pteron, wing) are 

 marked off from all other mammals by the possession of 

 wings, which are formed of skin stretched over the bones of 

 the arm, and including also the legs and sometimes the tail. 



