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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 Epeiroid 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.? 
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- 
Jey haps, most natural that the lower animals should seek to protect 
Origin of themselves within barriers formed by their body secretions, as is 
makes the case among the larve of many insects. The restless move- 
weaving Baye: mis 
Habit, ments 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 
Tube- delicate silk, which by its movements is pushed away from di- 
hai rect contact with its body, and hardens into the little case or 
arvee. A : : . 
pouch in which itself at last is encompassed. Thus we may 
suppose that, in an entirely natural way, the Supreme Overforce, while 
* 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 in declaring 
the general principle here announced. I have little doubt that subsequent studies of other 
species in all the tribes will verify the generalization. 
