668 



ACARINA. 



most degraded of the ordei' of Arachnids. It M'ill be seen that 

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

 ance of the larva? 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. 



Tardigkada Doyere. (Arctisca). The Tardigrades, or 

 Bear animalcules, referred b}^ some to the worms, were consid- 

 ered as mites by O. F. Miiller 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- 

 ni^a. 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 M3-obia, to consider the Tar- 

 digrades as a ftimily of mites. In 

 form, as indicated by the accompan3-ing 

 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. Miiller observed that they 

 moidted 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 worm with a large, fleshy 



Explanation of Plate 13.— Fig. 1, DermalHchus piri-puhescentis Pack., fe- 

 male. Frr,. 2, yonng male. FiG. 3, arlnlt male. Fro. 4, larva of TyjiModromus 

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

 (after Scheuten). Fig. (!, Ckcyletux seminivnru" Pack. Fig. 7, Sarcoptes scabiei 

 DeGeer (after Gervais). FiG. 8, Heternpnss ve.ntricosnx Newport, fnlly formed fe- 

 male. Fig. !», gravid female of the same (after Newyxirt). Fig. 10, Ixodes hovis 

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



