128 GENERAL ZOOLOGY 



mass of eggs closely swathed in soft " woolly" silk and 

 around this are two or three closely woven envelopes for 

 protection. A mother spider usually dies soon after her 

 cocoon is finished, but the young spiders, hatching within 

 the envelopes she has furnished, are able to endure the 

 winter and in the spring shift for themselves. The young 

 of some spiders hatch in the spring, others in the autumn. 

 Development within the egg usually requires only a few 

 days but spiderlings may remain inside the cocoon for 

 months. 



On a warm spring or autumn day you will often find 

 every tree and fence bearing long streamers of " cob webs." 

 These are the " balloons" of the young spiders. A co- 

 coon may produce fifty young and it would not be desira- 

 ble if they should all try to build orbs in the same bush. 

 This difficulty is avoided by the ballooning instincts of the 

 young. Soon after hatching they climb to some elevated 

 situation, each lets out a long streamer of silk, and then 

 jumps off into space (Fig. 59). The floating strands of 

 silk are carried by the wind and the spiders may travel 

 long distances. Thus each finds favorable hunting grounds, 

 remote from numerous brothers and sisters. Spiders pass 

 through a series of moults but there is no metamorphosis. 

 The young are much like adults in their general form. 



GENERAL REMARKS ON SPIDERS 



If spiders are compared with their remote ancestors 

 (Figs. 27, 28) it is apparent that they are highly specialized. 

 The race has acquired many improvements in structures 

 and methods. Though traces of segmentation are dis- 

 cernible in all the body regions, there are no free body 

 segments. To secure greater compactness and rigidity 

 all the segments have been united; the head and thorax 

 have also fused to form a single region, the cephalothorax. 

 The awkward abdominal appendages have been completely 

 lost, the heart has become restricted to the abdomen, and 

 there are many other evidences of racial specialization. 



