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THE POPULAR SCIENCE MONTHLY. 



other bear is largely a fruit, vegetable, and ] 

 insect feeder; but in the frozen north the 

 polar bear lives by necessity mainly on fish, 

 carrion, seals, walruses, and birds. Its no- 

 tion of an ' egg for breakfast ' is rather 

 amusing. It will clear an islet of eider-ducks' 

 eggs in a few hours." 



Dispersal of Fresh-water Shells. A re- 

 cent book by Mr. H. W. Kew deals with the 

 means by which fresh water and land shells 

 are dispersed. The occurrence of these 

 shells is sometimes very puzzling, as when 

 fresh-water shells are found in isolated 

 ponds. It is surprising how varied the 

 means of distribution are. The animals are 

 carried down stream on various floating ob- 

 jects. A case is cited by the author in 

 which a number of anodons were carried 

 away by a whirlwind and fell with the rain. 

 Canon Tristram found the eggs of a moUusk 

 attached to the foot of a passing mallard 

 which he shot in the Sahara a hundred miles 

 from water. A few instances have been 

 noted in which birds on the wing have been 

 shot with bivalves adhering to their toes. 

 Insects also lend their aid, and a water- 

 beetle has twice been captured on the wing 

 with Sphcei'ium attached to its legs. Another 

 specimen was caught with Ancyius attached 

 to its wing-case, and other aquatic insects 

 have been foimd with moUusks attached to 

 them. The actual process of transportation 

 of land shells has not often been observed. 

 Some live snails were once found in the 

 stomach of a wild pigeon three days after it 

 had been shot, and an operculated land 

 snail has been found dragged along on the 

 foot of a bumblebee on which it had caught. 

 An isolated dew pond after an existence of 

 ten years will generally yield several species 

 of fresh-water mollusca, and a mediaeval 

 fish pond has a considerable fauna. A church 

 or castle built of limestone, but surrounded 

 by non-calcareous desert, is for a large group 

 of land snails the equivalent of an isolated 

 pond ; but it is only on very old buildings 

 that one finds colonies of the special lime- 

 stone species. Mr. Kew also discusses the 

 dispersal of shells by human agency. 



Hearing of Infants. In her Notes on the 

 Development of a Cliild, issued in the series 

 of University of California Studies, Milicent 



W.. Shinn reports that the infant started vio- 

 lently while nursing, when a paper was torn 

 some eight feet away, on the third or fourth 

 day after birth, and at several times on that 

 and the few following days she started and 

 cried out even in sleep when a paper was 

 rustled sharply as her father sat by the bed. 

 During the first week she did not seem to 

 notice when on his return in the afternoon 

 her father sat close by, reading aloud or talk- 

 ing, but in the second and third weeks she 

 always became restless at this time. The 

 more modulated voices of women who were 

 in the room the rest of the time appeared 

 not to affect her at all. The sensitiveness to 

 sound seemed variable, for on the twenty- 

 third day, when Miss Shinn purposely rustled 

 paper near the baby, it produced no clear re- 

 action, nor did a table call bell struck sud- 

 denly and sharply at two feet and even one 

 foot from her head. On the twenty-seventh 

 day she showed no sign of hearing single 

 notes on the piano from the highest to the 

 lowest, yet she started at a hand-clap behind 

 her head. Ten days later, while the baby 

 was lying half asleep on Miss Shinn's lap, 

 the servant brought in a tin bath tub and 

 set it down abruptly so that the handles rat- 

 tled. The infant started violently with a cry 

 so loud that it brought in her grandfather 

 from two rooms away to see what was wrong. 

 She also put up her lip with the first crying 

 grimace she had ever made, and showed the 

 effect of the fright in a disturbed face for 

 five minutes. Yet throughout the first two 

 months there were also many times when 

 she failed to pay any attention to sounds 

 quite as striking as the few she did notice. 

 The great variation in sensibihty was espe- 

 cially noticeable in the second month. 



The Tropical Climate. Respecting the 

 climatology of tropical Africa, E. G. Raven- 

 stein represents that by ascending a moun- 

 tain we might, even in tropical Africa, enter 

 a region the mean temperature of which 

 coincided with that of Faigland ; but if we at 

 the same time considered the annual and 

 daily ranges of temperature, we should find 

 that a tropical climate differed exceedingly 

 from that of the temperate regions. In the 

 latter the annual range was considerable, the 

 daily range small. The character of a trop" 

 ical climate was the very reverse, for there 



