THE TARANTULAS 129 



no case do they reach the anal tubercle. In the typical tarantulas 

 and in all true spiders, the posterior segments are so much telescoped 

 or obliterated that the spinnerets and anal tubercle lie close to- 

 gether. In Heptathela the posterior median spinnerets are reduced 

 in size and fused into a single tiny colulus; so these spiders are usu- 

 ally said to have seven spinnerets. 



The internal features of the abdomen are also of particular in- 

 terest in this family. Five pairs of ostia are found in the heart of 

 Liphistius, the fifth pair belonging to the sixth somite, and this 

 number has not as yet been found in any other spiders. Although 

 Heptathela appears to have a more primitive external segmentation, 

 its ostia are reduced to four pairs, showing that the external fea- 

 tures have not kept pace with internal changes. 



The liphistiids differ from the atypical tarantulas in several 

 other respects than those enumerated above. The sternum is very 

 narrow and unmarked by sigilla. The eyes are well developed and 

 seem to be specialized rather than primitive, since the lateral ones 

 are enlarged and the anterior median very much reduced in size. 

 The coxa of the pedipalp does not have a maxillary lobe even 

 slightly developed; in this respect the liphistiids agree with the 

 majority of the typical tarantulas. 



The liphistiids live in burrows lined with silk, the entrance to 

 which is closed by a simple trap door of the wafer type sometimes 

 fastened down by the spider with threads from the inside. A num- 

 ber of lines of heavy twisted silk radiate from the lower lip of the 

 opening, serving as signal lines to warn the waiting spider of the 

 approach of insects. Sometimes the whole tube is set in the open 

 against the side of a wall, instead of being at least partially embedded 

 in the soil. The trap door and any exposed part of the tube is 

 covered with sand, thus to some extent camouflaged against the 

 natural background. Some of the liphistiids live in caves. The food 

 of these spiders usually consists of ground insects of various kinds, 

 but the cave-dwelling variety often subsist on a single species of 

 grasshopper or cricket. 



These primitive spiders are clumsy animals, which do not put 

 down dragline threads as do all other spiders. Ordinarily they as- 

 sume a stance with the front three pairs of legs directed forward, 

 an attitude suited to life in a narrow silken tube. They are said to 

 be awkward movers, and when "placed on their backs on a flat 

 surface cannot right themselves." 



