Araiieae. 1)1 



Order 4. — Araneae (Spiders). 



The carapace of the cephalothorax (prosoma) is unsegmented Table- 

 in the spiders, and the eyes are situated in tlie middle of its ^^^^o ^^' 

 anterior margin ; they are usually eight in number, and are 

 typically arranged in two transverse rows, JDut there are many 

 other arrangements in the various families. The first appendages 

 or chelicerae consist of two segments, the basal one of which 

 contains the poison-gland, whilst the apical one forms a retroverted 

 fang. All the remaining appendages are leg-like in form ; in the 

 male a complicated copulatory organ is present on the lower side 

 of the terminal segment of the second appendage or palp, k narrow 

 pedicel separates the cephalothorax from the " abdomen " (opis- 

 thosoma) ; with very few exceptions the latter is unsegmented, and 

 its lower surface is always furnished with a number of spinning 

 appendages. Two pairs of lung-sacs may be present, but the 

 posterior pair of these is replaced by tracheal tubes in most spiders, 

 and in a few species this is also the case with the anterior pair. 



Sound-producing organs, which are sometimes very complex in 

 structure, occur in a large number of Mygalomorph spiders. They 

 usually consist of arrangements of spines and rods which are 

 situated on the opposed surfaces of the basal joints of the anterior 

 limbs (either between the two chelicerae, or between the chelicerae 

 and tlie palps, or between the palps and the legs of the first pair). 

 The presence of a stridulatory organ in these bird-eating spiders 

 was first made known by Professor Wood-Mason in an Assamese 

 species [Chilobrachys stridulans). In this spider the inner surface 

 of the basal segment of the palp is furnished with a row of vibratile 

 bacilliform bristles and the opposed surface of the chelicera with a 

 number of strong spines. When irritated the spider assumes 

 a threatening attitude, raising itself upon its hind legs and 

 brandishing the front legs in the air, at the same time making an 

 audible rasping noise by rubbing together the basal segments of 

 the two anterior appendages. 



Another very similar type of stridulatory apparatus is present 

 in a number of the Arachnomorph spiders of tlie family Sicariidac 

 (in the genera Sicariiis and Scytodcs). The inner surface of the 

 femur of the palp in these spiders bears a single tubercle (or a 

 longitudinal row of tubercles), whilst the outer surface of the 

 chelicera is provided with a series of well-marked transverse ridges. 

 The noise made by the spiders of this family has been compared to 

 the buzzing of a bee. 



