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CLASS VI. AKACHNIDA. 



(MlTES.) 



THIS Class includes Spiders, Scorpions and 

 Mites; of which, numerous as they are, no species 

 was known to inhabit the British seas until the 

 discovery, a few years ago, by Professor Allman, 

 of a Mite living parasitically within the nostrils of 

 a seal. I have just added two species, still more 

 minute, and constituting a new genus, to our list of 

 marine AEACHNIDA. The latter are both found 

 crawling about sea-weeds at extreme low-water. 



The Class is for the most part composed of ter- 

 restrial animals ; but in the Order Acarina, to 

 which the three marine species above mentioned 

 belong, there is a large group which is aquatic ; 

 and many of them are sufficiently common in our 

 fresh-waters. 



The ARACHNIDA are distinguished by having 

 four pairs of jointed legs, by breathing air either 

 by lungs inclosed in bags, or by radiating pipes 

 (trachea), which communicate with the exterior by 

 means of slits (spiracles) on the surface of the 

 body, and by the concentration of their nervous 

 system. They have no antennae, and no compound 

 eyes ; their head and thorax are generally so united 

 as to be indistinguishable, but the abdomen is 

 generally separate. They are all carnivorous, and 

 many of them highly endowed with instincts and 

 powers for preying on other animals. 



