134 



HARDWICKE'S SCIENCE-GOSSIP. 



one point ; in which case the threads would join in 

 one, and so form but a single thread instead of a 

 band of many threads. As I can distinguish two 

 sizes of threads besides these bands (as shown in 

 the figure at a and b), I imagine that the bands 

 are the product of the third spinnerets, while the 

 two threads are emitted by the first and second 

 spinnerets. 



I now come to the spinning of the webs of the 

 Epeiridce. First let me correct an error in my former 

 paper. I stated, that when enveloping a fly in its 

 silken shroud, the spider employs silk from all six 

 spinnerets. This is incorrect; the first pair alone 

 is used. 



A good deal has been written about the way 

 spiders throw their threads across open spaces. 

 What force propels the threads I caunot say, but 

 how they go I can. One calm afternoon I was 

 amusing myself by keeping a spider on a short piece 

 of stick, by just winding up her thread as fast as 

 she let herself down. The thread when broken and 

 left hanging (mark this), showed no tendency to 

 blow out. But the spider got tired of my little 

 game, and after having several times, by breaking 

 the thread, dropped herself to the ground only to 

 be picked up again, she tried a new dodge. Still 

 hanging by her thread, she shot out several others, 

 each composed of many detached threads, which 

 blew about at once, and one of them catching in a 

 twig, the spider very coolly walked away. It seems 

 to me evident that a spider's thread when entire is 

 heavy enough to resist a gentle breeze; but when 

 the strands of which it is composed are separated, 

 even the slightest breath of wind has an influence 

 on it. 



It is on the spinning of the ordinary geometrical 

 webs, however, that I wish to say most. I pass 

 over the first stages of the process, because accurate 

 descriptions may be found in many books. After 

 all the radii have been set, the spider, beginning at 

 the centre of the web, draws round and round a 

 spiral thread until she reaches the circumference, 

 and then, commencing at some point in the circum- 

 ference, just reverses the process. This is in effect 

 the description which I have met with in several 

 books, and it is correct as far as it goes ; but then 

 it does not go far enough. The thread, which is 

 begun at the centre, and finished at the circum- 

 ference, has no viscid globules. But in a perfect 

 web all the circular threads are studded with these 

 sticky beads. How is this ? A garden spider can- 

 not walk over its web with impunity any more than 

 a fly can ; nor does it ever go on the sveb except to 

 catch a fly, and in so doing it breaks every viscid 

 thread on which it steps, being sufficiently strong in 

 the legs to avoid entanglement. Now the radii of 

 the web, towards their extremities, are too far apart 

 for the spider to step from one to another. So, in 

 making her web, she first spins a non-viscid thread, 



beginning at the centre and finishing at some point 

 in the circumference. On her return journey, when 

 leaving the viscid thread behind her, the divisions 

 of the previously spun plain thread are used as 

 bridges by which to get across the broad spaces 

 between the radii. Also, when this thread itself 

 was being spun, the parts of it already finished 

 served the same purpose, namely, that of enabling 

 the spider to step from one radius to another. The 

 reason for its being non-viscid is obvious : if it were 

 sticky, the spider could not walk on it. But it is 

 highly important that the completed web should be 

 as effective as possible for catching flies, and if the 

 threads were alternately viscid and plain its effi- 

 ciency would be much impaired ; therefore, as there 

 is no further use for the plain thread, the spider 

 bites off each division as soon as she has passed 

 over it, leaving only a small portion in the middle 

 of the web, and in this place she is wont to sit. 



Eor the reasons stated in the beginning of this 

 paper, I consider that the radii of the web are the 

 product of the first spinnerets ; the non-viscid spiral 

 thread the product of the second ; while the viscid 

 thread belongs to the third pair. 



Thus far my observations are straightforward 

 enough, but when, by means of dissections, I come 

 to consider the actual production of the viscid 

 globules, I am rather at a loss, and the little I can 

 make out tends considerably to upset the neat little 

 theory propounded above. 



I am inclined to think that the viscid beads are 

 produced by some apparatus independent of the 

 ordinary spinning-tubes on the spinnerets (which- 

 ever pair it may be that produces them), for these 

 reasons : Firstly, because by very careful rubbing 

 with a thread of glass the globules may be removed 

 from the spider's thread, which proves them to be 

 no constituent part of it ; and secondly, because I 

 cannot, with the most careful observation, detect 

 any difference in the spinning- tubes of spiders 

 which do and do not spin viscid threads sufficiently 

 great to account for the remarkable difference of 

 their threads. 



Now on the interior margins of the third spin- 

 nerets of every spider that I have examined, are 

 two spinning-tubes very much larger than their 

 neighbours. (See a, fig. 88, compared with b, and 

 also examine b t fig. 90.) These are briefly noticed in 

 Science-Gossip for 1874, page 181. They are 

 connected with two very large glands, which differ 

 somewhat in construction from the glands of the 

 small spinning-tubes. Eig. 90 shows the two large 

 tubes, and also part of the ducts (d) leading to the 

 glands : these are not represented, inasmuch as they 

 would take up too much space, for they would lie 

 below the common glands there figured, and be very 

 much larger. As it seems probable that in attach- 

 ing their threads to objects and in constructing 

 their cocoons all spiders require some viscid mate- 



