24 REPORT 108, U. S. DEPARTMENT OF AGRICULTURE. 



posterior part, the genital usually the larger. The legs are quite long and slender, 

 with a few scattered small hairs, and terminate in two claws with a median hairy- 

 brush beneath them. The hind coxae are often well separated from the anterior pairs, 

 but in Bddla they are approximate. 



The internal anatomy has been studied by both Karpelles and Michael. It is 

 peculiar in several respects. There is a large sac or diverticulum connected to the 

 oesophagus above, which Michael has termed the " receptaculum cibi, " and he believes 

 its purpose is to store the food for a short time. The 

 ventriculus ends blindly, there being no communication 

 to the anus. There are three pairs of glands in the ante- 

 rior part of the body, besides one large median gland. 

 One pair opens at the base of the mandibles; their func- 

 tion is unknown. Two pairs open into a common duct 

 which leads to the mouth; they are probably salivary 

 glands. The supra oesophageal and suboesophageal gan- 

 glia are more distinctly separated than in other mites 

 that have been examined. The pharjTigeal nerve 

 (which in other mites is single) in Bdella is split in two 

 parts. The male organs are remarkable for possessing 

 nl Ifl^ ^^x> ^^^ single and one pair of accessory glands, whose func- 



tion is little understood. In the female there is but one 

 oviduct. 



Triigardh has figiu-ed the egg of B. arctica Thor. (fig. 



20); it is nearly spherical, and with a number of long 



Fig. 19.— Venter of a Bddla. spines scattered over the surface. The larva and nymph 



(Author's illustration.) have much resemblance to the adult. They are never 



parasitic, and there is no sexual dimorphism, but the 



life history is not fully known. 



Several species of Bdellidse are common in the far north and have extended south- 

 ward along the coasts of both continents, and so have received a number of names. 

 Most of the forms seem to like the cold, and often occur in damp situations; they are 

 among the most common mites of the Arctic regions, while but 

 few are known from the Tropics. The species are usually red 

 in color, but some are blackish. They are predaceous in habit 

 and wander about in search of food — any small creature they J^^^- 

 can find. The palpi serve as tactile organs in most genera, 

 but in Cunaxa (fig. 23) they are used to capture and hold their 

 prey. These mites can run quite fast, and move backward as 



well as forward. Five genera have been recognized in this _ „ „ , „ , „ 



, f _,.,,. , . ^ ,_, FIG. 20.-Eseot Bdella. 



country, and one more {Scirula) is known in Lurope. Ihese ( vuthor's illustration.) 

 may be separated by the following tables: 



1. Mandibles chelate; two eyes each side; palpi geniculate, and ending bluntly 



in two or more long bristles 2 



Mandibles ending in one claw; no eyes, or only one each side; palpi not 



geniculate, and ending in a claw 4 



2. A median eye on front of the ccphalothorax ; tips of tarsi without plumose 



bristles Cyta. 



No median eye; tips of tarsi with one or two plumose hairs each side 3 



3. Last joint of palpus short, widened at tip Bdella. 



Last joint of palpus long, cylindrical Scirus. 



4. With eyes; palpus of three joints, and without spinelike bristles Eupalus. 



Without eyes; palpus of more than three joints 5 



5. Pal])i long, with spinelike bristles Cunaxa. 



Palpi short, thick, no spinelikc bristles Scirula. 



