No. 2.] PROTECTIVE RESEMBLANCES IN SPIDERS. 69 



young ichneumons ; and it is probable that spiders have no 

 more destructive enemies than these insects. 



FERTILITY OF SPIDEKS. 



As we have for some years made a practice of keeping 

 notes on all observations relating to spiders, whether they 

 touched on work on hand at the time or not, it happened that 

 we found ourselves, some time ago, in possession of a good 

 many facts concerning the number of eggs laid by diflferent 

 species. These numbers varied so greatly, running from forty 

 or fifty up to several hundred, as to excite considerable specu- 

 lation, on our part, as to the meaning of the variation. 



Why should one species lay eight hundred or a thousand 

 eggs, while another, equally common, laid onlj' fifty ? 



At about this time we had, in confinement, one male and 

 half a dozen females of the little ant-like spider, Synageles picata, 

 and before long each female made a cocoon containing three 

 eggs. This number was so small as to still further arouse our 

 interest and the idea suggested itself that a possible explanation 

 might be found in the principles laid down by Herbert Spen- 

 cer in regard to the inverse variation, in every species, of its 

 birth rate to the powers of self-maintenance possessed by its 

 individual members ; and that if this could be established it 

 would have a direct bearing on protective resemblances, since 

 one test of the advantage of its own peculiar modification to a 

 species might then be found in the number of eggs laid by 

 that species. 



To show how this doctrine bears upon the subject I will 

 briefly state Spencer's introductory considerations, and will 

 then quote at length from that part of his discussion which 

 applies to the point in question. 



The varying degrees of fertility among organisms result 

 from their conditions of life. We may class the actions which 

 affect each race of organisms as forming two conflicting sets. 

 On the one hand, by what we call natural death, by enemies, 

 by lack of food, by atmospheric changes, etc., the race is con- 

 stantly being destroyed. "On the other hand, (a) partly by the 



