thread to the spot on which he is stationed, 
by means of his fore feet, which are much 
arger and longer than the others, he darts on 
lis victim with such rapidity, and so true an 
lim, that he seldom misses it. He is pre- 
ented from falling by the thread just men- 
joned, which acts as a kind of anchor, and 
bles him to recover his station.”’"* Again, 
the kind of spider that has received the name 
f Geometric, “ having Jaid the foundation of 
x net, and drawn the skeleton of it, by 
ming a number of rays, converging to a 
ntre, next proceeds, setting out from that 
unt, to spin a spiral line of unadhesive web, 
e that of the rays, which it intersects, and 
sr numerous circumyolutions finishes this at 
e circumference. This line, in conjunction 
th the rays, serves as a scaffolding for her to 
alk over, and also keeps the rays properly 
fetched. Her next labour is to spin a spiral 
yrinthiform line from the circumference 
ards the centre, but which stops somewhat 
lort of it; this line is the most important part 
‘the snare. It consists of a fine thread, stud- 
‘ith minute viscid globules, like dew,which 
ir viscid quality retain the insects which 
the net. The snare being thus finished, 
@ geometrician selects a concealed spot 
h the vicinity, where she constructs a cell, in 
hich she may hide herself and watch for 
me; of the capture of which she is informed 
he vibrations of a line of communication, 
rawn between her cell and the centre of her 
3. Many animals are guided by instinct to 
or habitations for themselves, of very various 
inds, for protection against injury and against 
old, from the simple contrivance of the earth- 
brm, which closes the orifice of its hole with 
es or straw, up to the elaborate structures 
the bee, the ant, or the beaver. Here we 
ybserve a singular but easily understood diffe- 
ace between the inhabitants of water and air. 
the greater number of the more delicate animals 
lat inhabit the sea, chiefly of the Mollusca and 
fustacea, are provided by nature with shells, 
 Oryery firm integuments, evidently for protec- 
_ tion against the violence of the waves, in the 
_ formation of which instinct has little or no 
; but there are some of the Annelides 
habiting water, as the Sabella and Terebella, 
id the larvee of some moths, which have a sin- 
instinct enabling them to form habitations 
cient for their own protection, “ by collect- 
ing grains of sand ad fragments ot decayed 
_ Shells, &c. which they agglutinate together by 
| neans of a viscid exudation, so as to form a 
fm defensive covering, like a coat of mail.” 
his may be stated as the intermediate link be- 
veen the habitations given to the Mollusca and 
ea by nature, and those which many 
animals have organs and instincts enabling 
to form for themselves. 
manceeuvres of the terebella are best 
ved by taking it out of its tube and placing 
fg 
__* Kirby, vol. ii. p. 298. 
___ ¢ Ibid. p. 295. See also Darwin’s Zoon, vol. i. 
fae 
ee 
- 
INSTINCT. 
9 
it under water upon sand. It is then seen to 
unfold all the coils of its body, to extend its 
tentacula in every direction, often to a length. 
exceeding an inch and a half, and to catch, by 
their means, small fragments of shells and the 
larger particles of sand. These it drags to- 
wards its head, carrying them behind the scales 
which project from the anterior and lower part 
of the head, where they are immediately ce- 
mented by the glutinous matter which exudes 
from that part of the surface. Bending the 
head alternately from side to side, while it con- 
tinues to apply the materials of its tube, the 
terebella has very soon formed a complete 
collar, which it sedulously employs itself to 
lengthen at.every part of the circumference 
with an activity and perseverance highly inte- 
resting. For the purpose of fixing the different 
fragments compactly, it presses them into their 
places with the erected scales, at the same time 
retracting the body. Hence the fragments, 
being raised by the scales, are generally fixed 
by their posterior edges, and thus, overlaying 
each other, often give the tube an imbricated 
appearance. 
“‘ Having formed a tube of half an inch or an 
inch in length, the terebella proceeds to burrow ; 
for which purpose it directs its head against the 
sand, and contracting some of the posterior 
rings, effects a slight extension of the head, 
which thus slowly makes its way through the 
mass before it, availing itself of the materials 
which it meets with in its course, and so con- 
tinues to advance tili the whole tube is com- 
pleted. After this has been accomplished, the 
animal turns itself within the tube, so that its 
head is next the surface, ready to receive the 
water which brings it food, and is instrumental 
in its respiration. In summer the whole task 
is completed in four or five hours; but in cold 
weather, when the worm is more sluggish, and 
the gluten is secreted more scantily, its progress 
is considerably slower.’”’* 
The habitation formed by the water-spider, 
which is not exposed to the violence of the sea, 
shews much greater delicacy of workmanship, 
as well as greater variety of instinct. 
“ The insects that frequent the waters,” says 
Kirby, “ require, as well as those that inhabit 
the earth, predaceous animals to keep them 
within due limits, and the water-spider is one 
of the most remarkable on whom that office is 
imposed by the Creator. To this end her in- 
stinct instructs her to fabricate a kind of diving- 
bell, for which purpose she usually selects still 
waters. Her house is an oval cocoon filled 
with air, and lined with silk, from which 
threads issue in every direction, and are fast- 
ened to the surrounding plants ; in this cocoon, 
which is open below, she watches for her prey, 
and even appears to pass the winter, when she 
closes the opening. It is most commonly en- 
tirely under water, but its inhabitant has filled 
it with air for respiration, by which she is ena- 
bled to live in it. She conveys the air in the 
following manner: she usually swims upon her 
back, when her abdomen is enveloped in a 
* Roget’s Bridgewater Treatise, vol. i. p. 279. 
