I . D. SOAK : NOTES AND OBSERVATIONS ON 



Dytisci kepi as pets, and said he had often scrubbed dirty ones, 

 before introducing them into his aquarium, with a toothbrush, 

 but it did not dislodge the little red parasites he found on the 

 \. Mtr.il surface. Sometimes one finds a Dytiscus crowded with 

 parasites, but of different sizes. How is this to be accounted for? 

 Are they attacked time after time as a fresh batch of larvae 

 comes along, or do some secure more nourishment than others and 

 thrive accordingly? Figs, i and j are Nepa cinerea, another 

 favourite host for water- mites, drawn so as to show both surfaces, 

 and giving some idea of the number of parasites this species often 

 carries. It will be seen that the ventral surface is very badly 

 attacked. Fig. k shows a mite dislodged. In this case the legs 

 have nol fallen away, perhaps the creature has never been in a 

 favourable position to have them rubbed off. Water-mites 

 parasitic on aquatic insects were known before Midler wrote his 

 book in 1781, but they were then supposed to be the eggs of some 

 water-mite, and not a parasitic stage of the larval form. Duges, 

 I believe, in 1834, was the first to illustrate the larva of 

 Uyd/rachna globosa in its parasitic form on Nepa, and its nymph 

 and adult stages. 



The next genus we will notice is Hydryphantes. Mr. Browne 

 sent me last year a fly which had an orange-red parasite wedged 

 between the thorax and abdomen (Plate 29, fig. b). I managed 

 to get the greater part of the parasite away, and found it to 

 be one of the Hydryphantes. I was now very curious to find 

 out of what species was the fly, for I could not understand 

 finding fresh-water mites parasitic on anything but an aquatic 

 insect. Mr. Austin, of the Natural History Museum, kindly 

 named it for me. He said it was Caenia obscura, Mg., of the 

 family Ephydridae, and that it bred in the stems or leaves of 

 water-plants. This was sufficient to account for the presence 

 of a fresh-water mite on such a strange host. Our member 

 Mr. Wesche kindly drew the fly for me (Plate 29, fig. a). There 

 is another instance of Hydryphantes being parasitic, and that is 

 on Paludina cemtecta, Carl Thon, 1899. 



The genus Atax is one that has helped us very considerably 

 with information as regards its parasitic life. The species A tax 

 ypsilophcrusi A. bonzi, and others, are always found parasitic in the 

 fresh water mussel. The two species named I have never found 

 free-swimming at any time of the year, although I have collected 



