G68 



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 larvffi of the higher mites, such as Typlilodromus. 

 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. Midler in 1785, and a species was de- 

 scribed b}^ 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- 

 naea. With Miiller we would consider 

 them as insects belonging to the Aca- 

 rina, and 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 Do3'ere's valuable 

 memoir, they are essentiall}' mites, and 

 allied in form to Demodex and He- 

 teropus, though in their internal organi- 

 Fig. 643. zation diflering from all other insects 



in being true hermaphrodites. Miiller observed that they 

 moulted their skins. The mouth is adapted for sucking, 

 with stjde-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 chiAvs (in these characters 

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



Explanation of Plate 13— Fig. 1, Dermaleichus pici-pubescentis Pack., fe- 

 male. Fir,. 2, young male. Fig. 3, ailult male. Fig. 4, larva of Typlilodromus 

 pijri Sclieiiten (after Schouten). Fig. 5, larva of another species of Ti/phlodromus 

 (after Scheuten). Fig. C, Cheyletua seminivorus Pack. Fig. 7, Sarcoptea scdbiei 

 BeGeer (after Gervais). Fig. 8, Heteropus ventricnmis Newport, fully formed fe- 

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

 Riley. Fig. 11, Ixodes unipunctata Pack. All the figures are enlarged. 



