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Myobia of the mouse and mole. It is interesting to find this 

 relationship between the parasites of the mouse and bat, consider- 

 ing how closely-allied (zoologically) these creatures are, and how 

 widely different are their habits. In the Myobia the front pair of 

 legs are short, and armed, not with claws of the ordinary form, 

 but with large, strongly-curved, chitinous blades, which curl round 

 a chitinous peg, holding a hair of the mouse or bat between the 

 two, and forming one of the most efficient organs for the purpose 

 which I know of. In the Listrophus of the mouse and rat the hair 

 is held by a somewhat similar apparatus, formed, not by the claw, 

 but by the edge of the largely-developed and flexible maxillary lip ; 

 and, again, in the Hypopi of the Glyciphagus (Dermacarus) of 

 the squirrel and the mole it is the recurved posterior edges of the 

 dorsal and ventral plates, where they overlap, that perform the 

 same office of holding the hair. Most, but not all of these are 

 true parasites, living all their lives upon the same host, and feeding 

 upon him. Very different in kind is the parasitism of the great 

 sub-family of Analgince or Dermaleichi, which live their whole 

 lives upon the feathers of birds, and die if removed for any length 

 of time ; but they do not feed upon the substance of their host, they 

 simply serve to keep his feathers clean ; at least this is the opinion 

 of those who have studied the group, and it is upon this fact that 

 the name Analges is founded. The universality of the law was 

 stoutly disputed by a South African ostrich farmer, with whom I 

 once corresponded, who declared that the Dermaleichi increased in 

 such numbers upon his ostriches that if the parasites were not 

 killed (by sulphur, &c.) the birds died. If, however, they be 

 beneficial, as is apparently the case in the majority of instances, 

 they would then belong to Van Beneden's " mutualists," and not 

 be classed by him amongst parasites at all. The number and 

 variety of species in this group are very great ; they are most 

 imperfectly known, although the researches of Dr. Trouessart 

 among the bird-skins in the French Museums have lately made us 

 acquainted with a very long list of them. The occasional enormous 

 development of one pair of legs, and the strange forms of the 

 hinder extremity of the abdomen in the males of many of these 

 Acari, would hardly be believed without being seen ; but probably 

 the most interesting circumstance about them is that the female is 

 fecundated before the last change of skin, and that the egg-bearing 



