INSTINCT. 



a thread to the spot on which he is stationed, 

 by means of his fore feet, which are much 

 larger and longer than the others, he darts on 

 his victim with such rapidity, and so true an 

 aim, that he seldom misses it. He 13 pre- 

 vented from falling by the thread just men- 

 tioned, which acts as a kind of anchor, and 

 enables him to recover his station.' 1 * Again, 

 the kind of spider that has received the name 

 of Geometric, " having laid the foundation of 

 her net, and drawn the skeleton of it, by 

 spinning a number of rays, converging to a 

 centre, next proceeds, setting out from that 

 point, to spin a spiral line of unadhesive web, 

 like that of the rays, which it intersects, and 

 after numerous circumvolutions finishes this at 

 the circumference. This line, in conjunction 

 with the rays, serves as a scaffolding for her to 

 walk over, and also keeps the rays properly 

 stretched. Her next labour is to spin a spiral 

 or labyrinthiform line from the circumference 

 towards the centre, but which stops somewhat 

 short of it ; this line is the most important part 

 of the snare. It consists of a fine thread, stud- 

 ded with minute viscid globules, like dew,which 

 by their viscid quality retain the insects which 

 fly into the net. The snare being thus finished, 

 the little geometrician selects a concealed spot 

 in the vicinity, where she constructs a cell, in 

 which she may hide herself and watch for 

 game; of the capture of which she is informed 

 by the vibrations of a line of communication, 

 drawn between her cell and the centre of her 

 snare."f 



3. Many animals are guided by instinct to 

 form habitations for themselves, of very various 

 kinds, for protection against injury and against 

 cold, from the simple contrivance of the earth- 

 worm, which closes the orifice of its hole with 

 leaves or straw, up to the elaborate structures 

 of the bee, the ant, or the beaver. Here we 

 observe a singular but easily understood diffe- 

 rence between the inhabitants of water and air. 

 The greater number of the more delicate animals 

 that inhabit the sea, chiefly of the Mollusca and 

 Crustacea, are provided by nature with shells, 

 or very firm integuments, evidently for protec- 

 tion against the violence of the waves, in the 

 formation of which instinct has little or no 

 share ; but there are some of the Annelides 

 inhabiting water, as the Sabella and Terebella, 

 and the larvae of some moths, which have a sin- 

 gular instinct enabling them to form habitations 

 sufficient for their own protection, " by collect- 

 ing grains of sand and fragments ot decayed 

 shells, &c. which they agglutinate together by 

 means of a viscid exudation, so as to form a 

 firm defensive covering, like a coat of mail." 

 This may be stated as the intermediate link be- 

 tween the habitations given to the Mollusca and 

 Crustacea by nature, and those which many 

 land animals have organs and instincts enabling 

 them to form for themselves. 



" The manoeuvres of the terebella are best 

 observed by taking it out of its tube and placing 



* Kirby. vol. ii. p . 298. 



t Ibid. p. 295. See also Darwin's Zoon. vol. i. 

 p. 253. 



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 till 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 ; >n 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 Bridge-water Treatise, vol. i. p. 279. 



