SPIDERS. 



103 



In the BDELLID^ the palpi are five-jointed, the ocelli are sometimes absent, at 

 others they vary from two to six; the legs are long and stout. The mandibles are 

 chelate. Bdella, the principal genus, is represented in America by B. maritima a 

 species occurring under stones between tidemarks, and B. oblonga, which has been 

 found in Georgia under stones and the bark of trees, in rather moist situations. The 

 latter is a bright-red species. 



One frequently finds in the earth of gardens and conservatories small, slender-legged, 

 stout-bodied red mites, their surface greatly wrinkled, and presenting the appearance 

 of the softest velvet. Others are found upon plants. These are members of the 

 family TROMBIDILD.E. Under the microscope it is seen that they have claw-shaped or 

 needle-formed mandibles and short palpi. 



The genus Trombidium is represented in the United States by three known species, 

 scabrum, sericeum, and holosericum. All three of these forms are red, and live in the 

 ground, where they feed on the eggs of insects. Their labors in this line are so 

 important that T. sericeum is mentioned as a very efficient agent in checkino- the 

 ravages of the grasshopper. Another species, T. tinctoria, found in Guiana and 

 Surinam, furnishes a dye. The larval forms of some species of this 

 genus were formerly described under a distinct generic name, Astoma ; 

 these six-legged young are found living parasitically on other insects, 

 clinging around the base of the wings and sucking the blood of their 

 hosts. Larva? of other species have been described under the generic 

 name Leptus. Trombidium is easily recognized by its claw-shaped 

 mandibles, and by having the first pair of legs the longest. Tetrcu- 

 nychus has needle-shaped mandibles, the two anterior pairs of feet FlG - ^ j Astoma 

 widely separated from the posterior, and two ocelli. Tetranychus 

 telarius, a yellowish species with two red spots on the sides, is not uncommon on plants 

 in greenhouses and conservatories. 



The last family, PCECILOPHYSID^E, is of rather doubtful character. It was estab- 

 lished by the Rev. O. P. Cambridge for a minute form, one-third of a line in length, 

 from Kerguelen Island. Poecilophysis Jcerguelenensis has filiform palpi, which termin- 

 ate in a single claw, while the other legs are didactylous. Its describer thinks that it 

 combines characters of spiders, Solpugidae, chelifers, and Acari, and has erected for its 

 reception a possible new order, but other students of the Arachnida are inclined to 

 place it among the mites. 



ORDER II. ARANEINA. 



This, the second division of the Arachnida, contains the true spiders, and in its 

 treatment we use, by permission, the excellent work "The Structure and Habits of 

 Spiders," by Mr. J. H. Emerton, with such alterations and condensations as are 

 necessary to render it conformable to the space at disposal and the plan of the present 

 work. 



The common round-web spider, Epeira vulgaris, will serve to show the anatomy 

 of spiders in general. The body is divided into two parts, connected only by a narrow 

 joint just behind the last pair of legs. The front part of the body, called the cephalo- 

 thorax, contains the stomach, the central part of the nervous system, and the large 

 muscles which work the legs and jaws. The hinder half, the abdomen, contains the 

 intestine, the breathing-organs, the principal circulating-vessels, the organs of repro- 



