WATER MITES. 



^51 



timate large, and the last armed with spines. The feet are long 

 and slender and ciliated, except the two last, which are only pilose. 

 Its colour is pale red, and its size about that of a mustard seed. 



Genus Hydrachna. 



The genus is restricted by Duges to those fresh water mites 

 that have palpi with the third joint largest, a beak of the same 

 length as the palpi, and mandibles with 

 sharp blades. Their transformations 

 have been fully observed, and are very 

 interesting. From the eggs which have 

 been laid in spring in the stems of water 

 plants, perforated for the purpose, little 

 hexapod animals come to view, with a 

 large heart-shaped sucker in front, which 

 might be taken for a head, but that the 

 eyes are situate behind it on the anterior 

 margin of the back. Subsequently they 

 attach tJiemselves to different water 

 insects (Nepa, Ranatra, Dytiscus, &c.); 

 and whilst the abdomen is growing and 

 extending itself into an elongated sac, 

 the feet and the sucker remain of the 

 same size. After a time, however, the 

 feet drop off, and the creature remains 

 like a bag hanging from the insect to which 



it is affixed. For long these bags were thought to be the eggs of the 

 Nepa, and it was described as being like the frog of Surinam, that 

 laid its eggs on its ov/n back, and hatched them out of its skin. 

 This stage corresponds apparently to that of the pupa in other 

 insects, the perfect insect being formed within the skin, like a fly 

 in its pupa. The wood cuts show its various stages in the species. 

 Hydrachna globulus, now Hydrochoreutes globulus, a little further 

 on. 



Enlarged sketch of hinder part of 



abdomen of Nepa cinerea, with 



nymphs of Hydrachna adhering 



to it. 



