48 AMERICAN SPIDERS 



to break the cuticle of the leg, with the result that blood begins 

 to flow through the break. Although the spider may escape other- 

 wise unscathed, this is a most serious situation, inasmuch as an open 

 venous system allows the gradual draining of blood from the body 

 until death occurs. The instinct of the spider is immediately di- 

 rected to a preventive device. The leg is pulled out, and the flow 

 of blood is quickly halted at the normal breaking point between 

 coxa and trochanter. This amputation is accomplished with the 

 help of the remaining legs and the mouth parts. In some instances 

 the spider spins threads and ties the appendage to them, and is able 

 to amputate a whole leg or even a small stump and thus save itself 

 from almost certain death. 



Autotomy can be put to use by the spider to rid itself of an 

 appendage that is unwelcome for some reason other than injury. 

 The known males of the species of Tidarren have long been ob- 

 served to carry only one palpus, a great bulbous affair held in front 

 of the head. In the antepenultimate stadium, the palpi are only 

 slightly swollen, but after molting the creatures have two tumorous 

 enlargements resembling boxing gloves. So large are these new 

 members that the spider is handicapped by them, and is able to 

 manipulate them only clumsily. The obvious solution to the prob- 

 lem is the amputation of one of these palpi, and this is exactly what 

 the spider does, by a most interesting process. It spins a scaffold 

 of silk, similar to the molting sheet, and, suspended from it by its 

 legs, fixes one of its palpi in the threads. The spider now twists 

 around and around and, aided by pressure from its hind legs, twists 

 off the unwelcome palpus. The spider now has a single palpus, 

 which is held in front of the head and occupies much of the avail- 

 able space. At the next molt it becomes sexually mature, and the 

 vital parts of the palpus are revealed. A second palpus is never 

 regenerated to replace the old one. 



The spider's instinct to rid itself of an injured or inconveniencing 

 appendage takes precedence over all others, but once autotomy is 

 accomplished, the spider almost invariably does a most curious 

 thing. It picks up the bleeding member and sucks the juices from 

 it, usually discarding it only after it is sucked dry. This autophagy 

 is perhaps as old a habit as autotomy itself, but may not have any 

 especial significance beyond its general interest. Spiders often attack 

 each other, or other prey, and if successful only in securing a leg, 

 will stop and suck it dry in the same manner. The instinct asso- 



