668 



ACARINA. 



most degraded of the order of Arachnids. It will be seen that 

 the adult Demodex retains the elongated, worm-like appear- 

 ance of the larvae of the higher mites, such as Typhlodromus. 

 This is an indication of its low rank, and hints of a close rela- 

 tionship to the Tardigrades. 



TARDIGRADA Doyere. (Arctisca). The Tardigrades, or 

 Bear animalcules, referred by some to the worms, were consid- 

 ered as mites by O. F. Muller in 1785, and a species was de- 

 scribed by him under the name of 

 Acarus ursellus. They have also been 

 referred to the Rotatoria by Dujardin, 

 and were, by Schultze, considered as 

 parasitic Entomostraca allied to Ler- 

 nsea. With Muller we would consider 

 them as insects belonging to the Aca- 



r * na ' an( * venture ' after studying Clapa- 

 rede's admirable work, "Studien an 

 Acariden," containing an account of 

 the genus Myobia, to consider the Tar- 

 digrades as a family of mites. In 

 form, as indicated by the accompanying 

 figures, copied from Doyere's valuable 

 memoir, they are essentially mites, and 

 allied in form to Demodex and He- 

 teropus, though in their internal organi- 

 zation differing from all other insects 

 in being true hermaphrodites. Muller observed that they 

 moulted their skins. The mouth is adapted for sucking, 

 with style-like mandibles like those of Myobia. There are two 

 ocelli, and the worm-like body is cylindrical, consisting of four 

 thoracic segments behind the head, bearing four pairs of short, 

 thick legs, ending in three or four claws (in these characters 

 reminding us of the Peripatus, a worni with a large, fleshy 



EXPLANATION OF PLATE 13. FIG. 1, Z>ermaZeic7ms pici-pubescentis Pack., fe- 

 male. FIG. 2, young male. FIG. 3, adult male. FIG. 4, larva of Typhlodromus 

 pyri Scheuten (after Scheuten). FIG. 5, larva of another species of Typhlodromus 

 (after Scheuten). FIG. 6, Cheyletus seminivorus Pack. FIG. 7, Sarcoptes scabiei 

 DeGeer (after Gervais). FIG. 8, Hetqropus ventricosus Ne\vport, tally formed fe- 

 male. FIG. 9, gravid female of the same (after Newport). FIG. 10, Ixodes bovis 

 Kiley. FIG. 11, Ixodes unipunctata Pack. All the figures are enlarged. 



Fig. 643. 



