MITES. 289 



that probably yet remain to be detected by the 

 naturalist. Perhaps there is no species of bird, cer- 

 tain individuals of which may not harbour in their 

 plumage hosts of these little animated specks, con- 

 sisting of various kinds destined to feed on the 

 superabundant juices of the body. If so, how many 

 hundreds, one might almost say thousands, of species 

 of such Acari must there be of which we know 

 nothing ! And though some may think it trifling 

 to bestow much time or trouble in the investigation 

 of these atoms, yet it should be remembered that 

 our acquaintance with the entire scheme of nature 

 can only be advanced so far as we search into all the 

 varying forms of structure that occur, be the indivi- 

 duals in which they appear large or small. 



Sarcoptes passerinus* This is one of the more 

 common forms of Acari, parasitical on birds, and 

 remarkably distinguished by the disproportionate 

 size of the third pair of legs. It is well described 

 by Linnaeus, who, in reference to this circumstance, 

 says,-)* pedes tertii paris magni ; femora enim hujus 

 ambo simul mole ipsum corpus fere adcequant, reliquis 

 minimis : his monstrosis pedibus non incedit, sed modo 

 sese adfigit pennis vivacissima et agilissima avis, ne 

 excutiatur. In confirmation of this last remark I 

 observe, that, when placed upon a piece of white 

 paper, this creature in walking draws these enormous 

 legs after it as a dead weight, without attempting to 



* Acarus passerinus of Linnaeus. It is well figured by De 

 Geer, torn. vii. pi. vi. f. 12. 

 t Faun. Suec. p. 480. 



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