176 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



The greatest general simplicity of structure appears among the cocoons 

 of the Territelarise, Citigrades, and Saltigrades, and the Laterigrades nearly 

 approach them in this combination of simplicity and uniformity. 

 It may be said that the tribe which shows the greatest simplicity 

 plicity anc ^ uniformity of cocoon structure is the Citigrades. The in- 

 ference may therefore be drawn, that the greatest general sim- 

 plicity of structure exists among the cocoons of those spiders which have 

 them most closely under their personal care. It is manifest that in the 

 case of Lycosa and other genera that attach their egg sacs to their spin- 

 nerets and carry them about until their young are hatched, there is less 

 necessity for complex cocoonery to protect the enclosed eggs than in the 

 case of Orbweaving spiders, like Epeira or Argiope, who hang their cocoons 

 in the shubbery and leave them to the watch care of Nature alone. 



While this deduction is justified in the general view of the subject, it 



must be allowed that there are some exceptions which cannot well be 



explained. For example, the two cocoons which have absolutely 



the simplest structure are made by members of the Retitelarise, 



as Pholcus phalangioides and Steatoda borealis. The egg bags 



of the latter species consist of a mere pinch of silk of such sparse weft 



that the eggs are plainly seen through them. Pholcus, who carries her 



cocoon underneath her jaws, while she hangs continually upon her snare, 



holds her eggs together by little more than a netted bag of scant spin- 



ningwork. 



One who examines, even casually, these various forms will see that they 

 are determined substantially by the fact that the eggs, as they are extruded, 

 naturally form a spherical or hemispherical mass, according as 

 rigin i . ^j je y yj an g ree or Rre ov ip OS ited against some surface. Around 

 this mass the protecting spinning stuff is woven, and then the 

 external case. The addition of a foot stalk, more or less pronounced, ap- 

 pears to be determined by the act of suspending the cocoon during the 

 weaving thereof, and the subsequent covering in and thickening of the 

 suspensory cord so that the texture corresponds with the remainder of the 

 outer case. 



The little conical or pointed processes which characterize several cocoons, 

 as those of Tetragnatha and Uloborus, probably originated in the same way, 

 namely, by the attachment of suspensory or broken threads to various points 

 of the external surface, the points of attachment being thickened into little 

 puffs or rolls or points of spinning stuff. 



The introduction of extraneous material as an additional protection and 

 the encasing of the silken sack in mud, as with Micaria limicuiuv, is a 

 habit to be accounted for altogether outside of the above; but the fact 

 that these mud protected cocoons preserve the general form of the spin- 

 ningwork which encloses the eggs, is undoubtedly determined by the same 

 causes that regulate the shapes of all other cocoons. 



