42 Fresh-Water Mites. [Sess. 



This part at present is very little known or understood, or 

 what useful part they play in the economy of nature ; so, like 

 Muller, the man whose name I have mentioned so often, I 

 wish to induce others to take up and make a hobby of these 

 interesting little things. There is plenty of scope, as the 

 subject is not nearly exhausted. We in Great Britain are yet 

 a long way behind the Germans in our knowledge of water- 

 mites. Piersig and Koenike have done more work on the 

 subject than any previous writers. In America Mr R H. 

 Wolcott of Nebraska has written some splendid papers on 

 Atax and Curvipes (Fiona). Sig Thor in Norway is another 

 name well known to all who study Hydrachnids. 



I shall now show you a few drawings of British water- 

 mites : all those coloured have been drawn and coloured 

 while the creature was alive ; those without colour were 

 drawn from dead specimens. We have found in Great 

 Britain at present representatives of thirty-three genera, but 

 all the species have not been recorded which are known, I 

 thought, however, a few species just to show how great is the 

 variety in colour and form would be interesting, and perhaps 

 something new to the majority of the members. 



The first genus I will take is Arrhenurus, Duges — at one 

 time spelt without the h. This genus was introduced in 1834, 

 and several of Muller's species have been placed in it. It 

 contains, as I have said, the largest number of species, and 

 exhibits the greatest variety of form and colour. All are 

 hard-skinned and have skins like a coat of mail, and in some 

 cases with proper illumination under the microscope have 

 rather a metallic appearance. The males are quite different 

 from the females in structure, having the posterior margin 

 in some cases elongated backwards as much again as the 

 length of the body ; others have the body projected backwards 

 into two horn-shaped appendages, with a petiolus between. 

 Then again, there are some in which the posterior portion 

 has the appearance of a frill. Of course, these forms vary 

 in different species to any extent. Then as regards colour we 

 find some almost black, others blue, green, yellow, or brilliant 

 red. Eed, in both scarlet and crimson, in water-mites, is a 

 very favourite colour. 



Arrhenurus caudatus, De Geer (Plate III. fig. 1 : A, dorsal, 



