THE GENESIS OF SNAKES. 353 



tube is jirobably the most rudimentary form of nest. Moreover, the Tube- 

 weavers are quite generally thought by systematic arachnologists to include 

 the species that rank lowest in organization. Their characteristic web 

 might, therefore, witli considerable confidence be assigned the lowest place 

 in an order of industrial development. 



Our alignment of facts from this point will necessarily require the use 

 of the same material, only shifting the relative positions. But in the 



movements one may catch new views of the factors concerned, their 

 ^^„' values and relations. Let us, then, start with some form of 



tube as the typical snare and retreat of the spider in its most 

 rudimentary phase of life. At one end of the tribe of Tubeweavers we 

 find the most lowly organized families, such as Gnapho.sa, wlio limit them- 

 selves to simple tubes with the few lines which are necessary to lix them 

 to their surroundings. At the other extreme we find tlie highly organ- 

 ized and interesting spider, Agalena noevia, whose tube has developed from 

 its outer extremity into a widespreading sheet or pouch. This, again 

 (which is another manifestation of spinning habit), is supported by out- 

 going straight lines, which intersect each other at various points. 



If now we pass from the Tubeweavers to the Lineweavers, we observe 



that the sheeted snare, which forms so important a part of Aga- 



Tube- lena's web, appears as the sole snare of certain species of Liny- 

 weavers ,. J. IT-l- ^i.1 1- -1 



to Lii e P'^i^> ^^> foi" example, Lmyphia costata, who.se web is a simple 

 weavers, i^etted sheet with lines above and below to support it. Li other 

 words, it is the snare of Agalena minus the tube. 



Again, in the same genus of the Lineweavers, we observe that the inter- 

 secting lines, which are but a subordinate feature in the snare of Agalena, 

 are a prominent feature in such species as Linyphia communis and Liny- 

 phia marginata, which, however, also retain, but in a less developed form, 

 the sheeted portion of the snare. This part assumes the form of a bowl 

 in the one case, or of a dome in the other. The meshes of the spinning- 

 work lack the closeness of texture commonly observed in Agalena noevia 

 or the closely related Tegeiiaria medicinalis. 



Once more, in the same tribe of Lineweavers, we find that the inter- 

 secting lines of Agalena's snare appear in the genus Theridium, where they 

 are developed into a well organized mass of netted intersecting lines, form- 

 ing a formidable snare for the capture of insects. The position of the 

 spider within this web is entirely like that of Linyphia, and is wholly dif- 

 ferent from that of Agalena. 



It must be observed, however, that even in the case of Theridium the 

 intersecting lines have a strong tendency to approximate each other at the 

 central point where the spider rests, until, as in the case of Theridium 

 tepidariorum and Pholcus phalangioides, the spinningwork approaches 

 closely that of Linyphia's dome, and more remotely the sheeted spinning- 

 work of Agalena. 



