SCIENTIFIC SURVEY. 211 



especially during the frosts of autumn, when the changes produced 

 are greatest. All spiders are directly beneficial to agriculture by 

 their carnivorous habits, as they all prey upon insects, and do no 

 harm to vegetation. Their instincts are wonderful, and their habits 

 and organization worthy of more study than has yet been paid 

 them. We have no species poisonous to man, except when the 

 state of health renders the constitution open to receive injury from 

 their bite, just as musquitoes and black flies often cause serious 

 harm to some persons. 



The A rachnids are divided into two groups of families : First, 



PULMONARIA, 



which have pulmonary sacs for respiration, and six to twelve ocelli. 

 This group includes two families, one consisting of the true Spiders, 

 the other of the Scorpions. 



Araneidae. Spiders. Palpi simple pediform ; mandibulae armed 

 with a moveable and perforated claw, emitting a poisonous liquid. 

 The genera have been divided by Walckenaer : 



1. Into those that incessantly run or leap about the vicinity of 

 their abode to chase and catch their prey. Mygale hides in holes 

 in the ground or among stones. The largest spiders are found in 

 this genus. Filistata forms white silk tubes in walls and crevices 

 of rocks. Dysdera is found in silken tubes under ground. Segestria 

 makes silken tubes under the bark of trees. Lycosa is found under 

 stones, in holes, &c., bearing their cocoons attached to their anus, 

 and carrying their young on their back. The Tarantula of Italy 

 belongs to this genus. L.fatifera lives in holes nearly a foot deep. 

 These holes seem to be dug by the spider, and to be increased 

 gradually, as its size may require ; the opening has a ring of fila- 

 ments woven by the spider to prevent the filling up of the cavity 

 by rain. In Dolomedes the female of one species constructs a 

 web not unlike that of Tegenoria. They wander near streams or 

 ponds, often hiding under the surface of the water, or rambling on 

 trees. Sphasus makes no web, except when the female makes her 

 cocoon. The species wander in quest of prey about the trunks of 

 small trees, or upright trees, and when at rest, spread their feet 

 like many species of Thomisus. I have reason to think that the 

 young are carried on the back of the mother as in Lycosa. (Henfz, 

 in whose words most of these remarks are ii;iven.) Attus leaps 

 prodigiously after its prey. Some species closely resemble ants. 



2. Into those species which wander abroad and are incessantly 



