246 ROUND THE YEAR 



up the relation of these aerial excursions to the 

 life-history of the Spider. The circumstance that it is 

 largely though by no means exclusively immature 

 Spiders which take to flight connects this case with 

 the larval dispersal of very many marine animals. 

 The heavy-armoured adults which haunt our shallow 

 seas are obliged to keep near the same spot, and 

 dispersal is effected by the fresh-hatched larvae, which 

 often migrate before they have acquired a mouth 

 or stomach, and are provided with temporary loco- 

 motive organs for this very purpose. In the case of 

 land animals, where the weight of the body cannot be 

 supported by a dense medium, locomotion is too 

 difficult to be effected by very immature individuals, 

 and only full-grown animals migrate ; (Insects, Frogs 

 and Birds furnish plenty of examples) but for the 

 peculiar flight of Spiders small size is essential, 

 and this one circumstance may have determined 

 their deviation from the common practice of land- 

 animals. 



Spiders often protect their eggs by cocoons, which 

 may be laid in crevices or webs, or carried about by 

 the female. The fresh-hatched young often creep 

 about within such a cocoon or web for some days, 

 during which time they are watched over by their 

 mother. At last they begin to seek their own food, 

 which they procure by hunting. Probably no very 

 young Spider is able to make a snare. By the end of 

 summer, when food begins to be scarce, the young 

 Spiders set about the business of dispersal. It..is not 

 likely that they get much to eat until the following 

 summer, but this is a point on which we have few or 



