THE LIFE OF THE SPIDER 35 



After laying a mass of eggs, the female covers them with a silken 

 sheet and molds the mass into the egg sac characteristic of her spe- 

 cies. The eggs (Plate X) are ordinarily spherical, or broadly oval, 

 but their shape may be largely determined by their position in the 

 egg mass. A great many spiders cover the eggs with a viscid secre- 

 tion, which hardens and agglutinates the mass into a single body. 

 In some cases the eggs are only lightly agglutinated, held together 

 in a mass by a few threads, and thus retain nearly a spherical form. 

 Frequently, the weight of the mass is so great that the eggs assume 

 the shape forced upon them by the available space, and thus are 

 irregular in outline. The size of the eggs varies within rather wide 

 limits, being 0.4 mm. in some of the smallest true spiders, but at- 

 taining 4.00 mm. in the large tarantulas. 



The number of eggs laid by different spiders varies enormously. 

 The largest of all spiders, Theraphosa blondi, is reputed to lay as 

 many as 3000, and the large orb weavers and pisaurids, which fre- 

 quently spin more than a single egg sac, are credited with 2200 in 

 a single sac. At the other extreme we find many tiny spiders that 

 habitually lay only one, two, or very few eggs at a time, and per- 

 haps no more than a dozen during their lifetime. The average num- 

 ber for average spiders is in the neighborhood of one hundred. 

 Those habitually producing more than a single sac usually place 

 fewer eggs in each, so that the average is not greatly increased. 



There is a considerable correlation between the size of spiders 

 and the number of eggs they are physically capable of producing at 

 any one time. We expect the large tarantulas to be large egg pro- 

 ducers, and find it true, as is well shown by Baerg's average of 812 

 eggs per sac for one of the large southwestern American species. 

 The contents of five sacs varied from 631 to 1018. The sacs of these 

 creatures are tremendous flabby bags often 2 or 3 inches in diameter. 

 An unopened sac of Hapalopus pentaloris, a brightly colored and 

 curiously marked tarantula of moderate size, from Mexico, con- 

 tained 986 young and each of the babies measured about 3 mm. in 

 length. Only 288 eggs were found in a sac of Phormictopus can- 

 ceroides, a very large West Indian tarantula. Another unopened sac 

 of this same species was 2% inches in diameter and contained 252 

 eggs in the deutovum or second egg stage. The eggs of the first sac 

 measured about 4 mm. in diameter, and the deutova of the second 

 were about 7 mm. in length. 



Larger eggs are produced by spiders of greater size. The eggs 

 of Phormictopus are as large as small peas and exceed by several 



