THE PLACE OF SPIDERS IN NATURE 19 



borne diseases are Texas Fever of cattle and Rocky Mountain 

 Spotted Fever, a serious illness of man. 



Solpugids. The curious arachnids know as solpugids (Plate 4 

 and Plate VIII) are commonly encountered in the American South- 

 west, as well as in some of the northern states in the West. The 

 outstanding characteristic of these creatures is the great size of their 

 chelicerae, which are proportionately larger than in any of their 

 relatives. While feeding on their insect prey, they work the cheli- 

 cerae with a sawing motion, holding fast with one while they drive 

 the other in deeper. It is believed that they take only liquid food 

 from their prey and cannot eat pieces of any size. 



Most species live in arid regions, where they hide under stones 

 and debris, and come out at night to do their hunting. They are 

 swift creatures and for that reason have been called "wind scor- 

 pions" in the Near East and in Africa, where a great many large 

 species abound. Most American species are about an inch long, but 

 two or three are nearly double that size; with their long legs clothed 

 with reddish hairs, they have a formidable appearance. But, since 

 they possess no poison glands and cannot effectively use their tre- 

 mendous chelicerae on large objects, they need not be feared by 

 man. 



Ricinuleids. The curious, enigmatic arachnids of this group are 

 the rarest of all arthropods. They resemble ticks superficially in 

 general appearance, and further simulate the sluggish, deliberate 

 movements of the latter. The ricinuleids possess various peculiarities 

 of structure that set them apart from all other living arachnids, and 

 represent a group that was probably far more abundant in Car- 

 boniferous times than they are today. No true eyes are present in 

 the ricinuleids, but vague, pale spots on each side of the carapace 

 may well represent vestigial eyes. Appended to the frontal edge 

 of the carapace is a hood, the cucullus, which fits down tightly over 

 the chelicerae. The cephalothorax is narrowly joined to the abdomen 

 by a pedicel, but this is hidden from view by expansions of the 

 base of the abdomen, which fits very closely with the cephalothorax, 

 the juncture forming a coupling device. The living animal is able 

 to disengage the carapace from the abdomen so that the genital 

 orifice is exposed, and this action is necessary during egg-laying and 

 mating. In the males, the third leg is provided with a complicated 

 copulatory apparatus. It is presumed by analogy that the apparatus 



