204 



ANIMALS OF LAND AND SEA 



level or from the change of seasons, nor can they exist in 

 deeper water because there is not food enough. 



The polyzoans, hydroids and sponges are fixed animals having 

 representatives in fresh water; but in all these groups, in con- 

 trast to those just named (except for a 

 few mud swallowers) , some forms multi- 

 ply by fragmentation of the young which 

 in the sponges and the polyzoans in fresh 

 water is represented by the formation of 

 statoblasts or gemmules. 



The most important creatures in fresh 

 waters, aside from some of the larger and 

 deeper lakes, are the amphibious insects, 

 all more or less closely related to others 

 on the land. These mostly live as larvae 

 in the water and fly about as adults in 

 the air; but some are water livers at all 

 stages, though these, too, when adult 

 fly about at night. There are many 

 thousands of such insects, and you find 

 their larvae everywhere, even in brome- 

 lia leaves and pitcher-plants, and in tin 

 cans and flower vases. A list of them shows a formidable array.^ 

 Of these nearly all the caddis-flies, all the true flies except 

 some mosquitoes, the corethrids, tabanids, leptids, some crane- 

 flies and some stratiomyids, the weevils and the chrysomelids, 

 and the few pyraUd moths are vegetarians; a few of the flies 



Figs. SQi-593. The shell 

 of a Paper Nautilus. 



For explanations of the 

 figures see p. .xxx. 



^ They are the may-flies, the dragon-flies and damsel-flies, the stone-flies, the 

 alder-flies, the dobson-flies, and the caddis-flies, none of which are true flies at 

 all since they have four wings; numerous bugs, such as the giant water-bugs, 

 the water-scorpions, the notonectids, the water boatmen, the veliids, the water- 

 striders, and the hydrometrids; many flies, some tipulids or crane-flies, some 

 moth-flies, the dixid flies, mosquitoes, corethrids, most chironomids, the black- 

 flies, the blepharocerids, many stratiomyids and horse-flies or tabanids, some 

 leptids, a few syrphids, the tetanocerids, most ephydrids, and some others; 

 many beetles, such as the giant water beetles, whirlgigs, haliplids, hydrophilids 

 and parnids, some chrysomelids, and some weevils; and there are even some 

 pyralid moths and hymenopterous egg parasites. 



