THE LIFE OF THE SPIDER 35 



its large brown egg sac. The smaller Pisaurina mira had 518 in a 

 sac of average size. Bonnet records a total of 2292 eggs in the four 

 cocoons of the European Dolomedes fimbriatus, a species much 

 smaller in size than several American members of the genus. 



When multiple cocoons are spun by a single female, the number 

 of eggs is less in the later ones. A female of Aranea cornuta, which 

 made 10 sacs, laid a total of 1210 eggs, deposited in the following 

 order: 234, 218, 182, 140, 112, 87, 81, 72, 51, and 33. In instances 

 of this kind, some of the later eggs may be infertile, owing no doubt 

 to the exhaustion of the semen stored in the receptacles, and perhaps 

 also to its gradual loss of viability. In the later cocoons, the exhaus- 

 tion of the female is apparent in her spinning ability, which becomes 

 progressively less perfect. In order to maintain the normal popula- 

 tion of a species, spiders produce a sufficient number of eggs to cope 

 with all the factors of the environmental resistance, and emerge 

 with a pair for each one in the normal population. The female 

 Argiope aurantia lays 1000 eggs, covers them with a tough cocoon, 

 and yet has an average survival from the large number of only one 

 pair. Peckhamia picata lays a few eggs, placing them at different 

 places in 3 or 4 cocoons, and still maintains an average population. 



THE EGG SACS 



The essential work of the female is completed when she has laid 

 her eggs and enclosed them in some kind of silken sac. This act 

 frequently represents the last effort of the mother in behalf of a 

 new generation she may never see. But though early death is the 

 lot for many, it may be delayed long enough for the mother to 

 guard the cocoon for a limited period and even to aid in some way 

 the emergence of her brood. In some species, the female spins more 

 than one sac and must then dispose of the others in her web or hide 

 them away, in order to give her time to the newest sac. 



In the contents of the sac rest the hopes of the whole species 

 for survival, so it is not surprising that considerable attention may 

 be given to the fabrication of the covering. Many egg sacs are 

 strongly made, beautifully designed creations, often pleasingly tinted 

 with colored silk. Especially constructed for her eggs by the female 

 spider, the egg case is fundamentally different from an insect co- 

 coon, which is the covering the larval insect spins around itself and 

 in which it transforms. The degree of perfection of the sac is cor- 



