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number of these hairs is very great, as on the legs of the water 

 gnat (Hydrometra stagnorum), the whole limb becomes coated 

 as it were with a layer of atmospheric air, which prevents it 

 from sinking below the surface of water. From the same 

 cause a fly is enabled for a short time to creep upon fluids : 

 that it cannot do so as well as the other insect, depends upon 

 the different conformation of the limb ; in one case the foot 

 alone is brought into operation, in the other more than half 

 the leg. 



It has been remarked by some observers, that, by dipping 

 the feet in alcohol, the power of walking on water is lost. 



This is readily explained by a reference to cotton wool and 

 a variety of other substances, which have a strong affinity for 

 gaseous elements. 



They cannot be moistened with water without much pres- 

 sure or trituration, but are saturated at once by spirit of 

 wine, and will then take up water without any difficulty. 

 Some observers have explained the phenomenon by supposing 

 the secretion of the foot was insoluble in water, and had a re- 

 pulsive power towards that fluid; that this secretion was 

 dissolved away by the alcohol^ and that the water consequently 

 could come into immediate contact with all parts of the leg, 

 and the power of walking on the water would be destroyed by 

 the limbs sinking into it. 



It is really immaterial which explanation is correct — there 

 is probably truth in both. 



In the large blue bottle fiy, the blow fly (musca vomitoriaj, 

 the dung fly, and the chequered blow fly, the same apparatus 

 exists as in the smaller variety, but we find an important and 

 interesting addition. 



We can readily imagine, that as the hairy flap has no internal 

 framework for its support, the larger its size the less its use- 

 fulness would be — there would be a constant tendency for the 

 free end to fall down, like a sheet of paper held horizontally 

 by one corner only. This would doubtless be the case were it 



