INVEBTEBRATA. 413 



Family II. PEDIPALPI. 



This group is composed, according to Cuvier, of two 

 satanic genera, Tarantula and Scorpio. The species of 

 these genera are described as malignant and venomous; 

 but they do not exist in temperate or northern latitudes. 



ORDER II. TRACHEARIJE. 



This order differs in organs of respiration and circulation 

 from the foregoing. It is divided into those "furnished 

 with chelicera, two fingers of which are movable," and into 

 those in which "these organs are replaced by simple laminae, 

 or lancets, which, with the ligula, constitute a sucker." These 

 animals are very small. 



First family of Cuvier, Pseudo-Scorpiones, is terrestrial, 

 and composed of two genera, Galeodes and Chelifer. 



Second family, Pycnogonides. These are marine animals. 

 "They are found among marine plants, sometimes under 

 stones near the beach, and occasionally also on the cetacea." 



Third family, Holetra. This consists of two tribes, 

 the Phalangium and the Acarus. The first "live on the 

 ground at the foot of trees, and on plants, and are very 

 active; others conceal themselves under stones and moss." 

 The second, Acarides, is composed of genera Acarus, Trom- 

 bidium, and Ixodes. The first, small microscopical, includes the 

 itch insect,* the " arcari of the human psora," and the mites, 

 which are "excessively prolific." The second, Trombidium, 

 contains the subgenera Erythrseus, Gamasus, Cheyletus, Ori- 

 bata, Uropoda, etc. This is the group to which the common 

 Tick belongs, or the subgenus Ixodes. Of the Ixodes, Cuvier 

 remarks : " They are found in thick woods, abounding in 

 brush, briars, etc. They hook themselves to low plants by 

 the hind legs, keeping the others extended, and fasten to dogs, 

 oxen, horses, and other quadrupeds, and even on the tortoise, 

 burying their suckers so completely in their flesh that they 

 can only be detached by force." 



* Sarcoptes scabiei. "Itch is caused probably by different spe- 

 cies of Sarcoptes." H. 



35* 



