INTRODUCTION. XV. 



By moan8 of this instrument tho silk is carded or teased out, so 

 as to become very flocculont and adhesive ; it is then disposed 

 about the lines of the snare for tho purpose of entangling tho 

 spider's prey. 



Spiracular Plates and Breathing Organs. 



Beneath tho fore extremity of tho abdomen are two, generally 

 very distinct, roundish or oval platos, placod in a transverse line, 

 (pi. i., fig. 1, e,e, and fig 11, b,b). In some spiders — Thera- 

 phosidos and Di/sderidss — these are four in number, the two 

 additional ones succeoding the others a little way towards tho 

 middle of tho abdomen (pi. ii., fig. 2, «',«', c\c\ and fig. 1, a,a, 

 b,b). At the postorior-margin of each of these plates is a trans- 

 verse slit-like opening, leading to the main breathing organs, 

 which are situated underneath. Those organs are a modification 

 of the tracheal system found in the Insecta. Instead of the 

 air being taken (as in that class) into simple tubes from numer- 

 ous external orifices, and so distributed over the body for tho 

 aeration of the vital fluid ; it is taken in through the transverse 

 slits, mentioned above, into a special breathing apparatus ; thus 

 localizing the main supply of air, in a way somewhat 

 analogous to the action of the lungs of the mammalia, and 

 thence aerating the vital fluid as it passes out of the dorsal 

 vessel, or heart. There are, however, in many spiders, other 

 orifices leading, probably, to simple air-tubes (or tracheae) in 

 different parts of the abdomen. One of the most noted instances 

 of this, among British spiders, occurs in the genus Awjphmna 

 Sund. (pi. i., fig. 11, c.J Anothor remarkable instance is in the 

 genus Cambridgea, L. Koch., found in New Zealand. 

 Genital Aperture. 



One other portion of the abdominal structure must be shortly 

 noticed — the genital or sexual aperture. This is situated 

 exactly between the openings of the breathing apparatus, and 

 leads to appropriate internal organs. In the male sex the 

 fecundating fluid is secreted in these organs. The curious office 

 of tho palpi of male spiders, as instruments for the reception 

 and application of this fluid, has boon already described. 



