NEST MAKING : ITS ORIGIN AND USE. 329 



frame, by this vertical movement drawing out the thread and beating it 

 back again, thus thickening the weft upon the lines. In this manner a 

 sheet of thin texture is rapidly formed, and this, in the course of time, is 

 thickened by a repetition of the same mode of spinning. This is exactly 

 the method, as I have heretofore shown, pursued by Argiope cophinaria 

 in thickening her shield. (See Chapter VI. and illustrations.) It is the 

 manner in which the dome like tents of all the Epe'iroid spiders are con- 

 structed. When the method of procedure has been ascertained in one 

 spider, the arachnologist may be assured that he has the key to the 

 methods practiced among all the tribes. 1 



IV. 



The tube making faculty appears to be, as far as secondary causes are 

 concerned, the natural result of the instinct of self protection. It is, per- 

 haps, most natural that the lower animals should seek to protect 

 Origin of themselves within barriers formed by their body secretions, as is 

 the case among the larvae of many insects. The restless move- 

 Habit, merits of the body, characteristic of these creatures, conjoined 

 with the instinct to cover themselves up, to protect themselves 

 from unfavorable weather changes and from the approach of enemies, 

 may be a sufficient natural explanation of the origin of the tube making 

 habit. 



Thus, the silk moth larva, while secreting silk from the glands which 

 open on the upper lip, moves backward and forward, continually distribu- 

 ting its secretions, and at the same time, by the motion of its body, limits 

 them to the borders of the space around which it moves. In the same 

 way the social caterpillars have learned to shut themselves within their 

 well known tent, which presents so largely the appearance of a designed 

 structure, but which, in its origin at least, may have been quite as much 

 the result of accident, the silken secretion simply hardening around the 

 limits of the space through which the restless creatures move, and which 

 by their motions they keep free from threads. 



In like manner the larva of the ant, at the moment when nature brings 



upon it the sense of the great change from its larval to its pupal state, 



moves backward and forward within a narrow space, secreting its 



delicate silk, which by its movements is pushed away from di- 



T rect contact with its body, and hardens into the little case or 



pouch in which itself at last is encompassed. Thus we may 



suppose that, in an entirely natural way, the Supreme Overforce, while 



1 It took many years of observation, numberless experiments by day and throughout 

 many nights of careful watching among the various species, to reach this conclusion. But I 

 am so confident that I have fully demonstrated it, that I have no hesitation hi declaring 

 the general principle here announced. I have little doubt that subsequent studies of other 

 species in all the tribes -will verify the generalization. 



