1008 INSECTS AND ARACHNID A 



it has been confirmed by the subsequent investigations of Mr. 

 Lowne. 1 



The Arachnida, or scorpions and pseudo-scorpions, and the Ara- 

 neida or spiders, present much that is of interest even to the unscien- 

 tific who use the microscope only for pleasure. The general remarks 

 which have been made in regard to insects are equally applicable 

 to these, but have special application in that group known as the 

 Acarina, consisting of the mites and ticks. Some of these are 

 parasitic, and are popularly associated with the wingless parasitic 

 insects, to which they bear a strong general resemblance, save in 

 having eight legs instead of six. The Acarina are the true * mites ; ' 

 they generally have the legs adapted for walking, and some of them 

 are of active habits. The common cheese-mite, as seen by the naked 

 eye, is familiar to every one ; yet few who have not seen it under a 

 microscope have any idea of its real conformation and movements ; 

 and a cluster of them, cut out of the cheese they infest, and placed 

 under a magnifying power sufficiently low to enable a large number 

 to be seen at once, is one of the most amusing objects flint can be 

 shown to the young. There are many other species, which closely re- 

 semble the cheese-mite in structure and habits, but which feed upon 

 different substances ; and some of these are extremely destructive. 



The Acarina are the smallest of the Arihropoda, arid are specially 

 well fitted for microscopical examination ; indeed, with the exception 

 of the Ixodidce (including the Argosince), which attain a substantial 

 size, particularly in tropical countries, but little can be learnt 

 respecting them without such aid ; as far as is at present known, 

 other mites are not larger in hot countries than in Europe. Mam 

 species make beautiful objects for the microscope, and may be well 

 preserved, the hard-bodied specimens in balsam without heat or 

 pressure, the soft-bodied in glycerin or glycerin jelly ; e.g. the 

 nymphs of Leiosoma palmacinctum, Tegeocranus cepheiformis, T. 

 dentatus, and the adults of Glyciphagus pliimiger and G. palmifer 

 are admirable. They are all British, and are found respectively on 

 lichen at the Land's End, on the fallen bark and needles of fir-trees, 

 on fallen oak-wood, in the fodder in stables, and on cellar- walls. 

 Many of the Trombidiidw and Hydrachnidce also are very beautiful ; 

 and the Dermaleichi, especially the males, and such creatures as 

 Myobia, Listrophorus, tfoc., are extremely curious. With the excep- 

 tion of the Pnytoptidce, all Acarina in the adult stage have eight 

 legs and the constriction between cephalo-thorax and abdomen is 

 far less marked than in insects and spiders in many genera it is 

 wholly lost. The sexes are distinct and often very different from 

 each other ; the reproduction is oviparous or ovo-viviparous pos- 

 sibly in rare and exceptional instances viviparous. The ova are 

 usually elliptical or oval ; in those which have a hard shell a 

 curious stage known as the ' deutovium ' exists ; as the egg increases 

 in size the shell splits into two symmetrical halves, which remain 

 attached to the lining membrane, but are widely separated, the 



1 Keference should be made to Professor Btitschli's observations in Morplwl . 

 Jahrbttch, xiv. p. 170, and Dr. Voeltzkow's paper in Arbeit. Zool. Zool. Inst. Wiir;.- 

 burg, ix. p. 1. 



