No. 2.] PROTECTIVE RESEMBLANCES IN SPIDERS. 71 



dangers to be met as a constant quantity ; then, as the abihty 

 of any species to meet them must be a constant quantity too, 

 and as this is made up of the two factors — power to maintain 

 individual life and power to multiply — these cannot do other 

 than vary inversely: one must decrease as the other increases."* 



To make a fair application of this to spiders — to determine 

 with any degree of certainty whether the spiders that lay a 

 large number of eggs are poorly equipped for individual main- 

 tenance, while those that lay a small number are well equipped, 

 we ought to have many more facts than are at present availa- 

 ble about the conditions of life in the different species. It is 

 interesting, however, to see how what facts we have accord with 

 the theory, and, supposing the theory to be correct, to see which 

 forms of protection are most successful. 



To take two species from the same family, we have no 

 other Epeirid which lays so many eggs (500-2,200) as Argiope 

 cophinariaf and no other which lays so few (34) as Tetragnalha 

 laboriosa. According to the theory, cophinaria should be ill equip- 

 ped for the battle of life while laboriosa should be in much closer 

 harmony with its relations. 



Both depend upon their webs for their food supply and 

 probably both secure as much as they need, so that their 

 advantages in this respect may be considered equal. J 



In regard to their means of protection from enemies, a 

 first view of the two spiders would seem to favor our theory. 

 The slender, elongated form, the greenish-golden color, blend- 

 ing with that of the leaves, the habit of clinging, with legs 

 extended in a line with the body, close to the branch upon 

 which it rests, all combine to render laboriosa inconspicuous. 

 On the other hand, we have in the great cophinaria, dressed 



* Principles of Biology, Vol. II, p. 396, et seq. 



^ A. riparia Eentz. 



I The zig-zag band of white silk which runs up and down through the middle of 

 the cophinaria web Is used in the capture of prey by a relation of our spider in Mada- 

 gascar. It serves as a reserve line with which to tie up any extraordinarily large 

 Insect, such as a grasshopper, when he becomes entangled in the web. Cophinaria, 

 however, is not known to make this use of it, its only usefulness to her being the added 

 strength which it gives to the web. Vinson, loc, cit., p. xv. 



