THE LIFE-HISTORY OF FRE8H-WATEK MITES. 365 



at places where I know there are plenty of mussels with the 

 parasites inside. Of course, they must leave the mussel-shell at 

 some time or another, or how is it that we find them more or less 

 in all mussels? A number of writers have described the 

 parasitic stage of Atax. Van Beneden in 1848 published a very 

 fine paper, with figures showing the whole life-history of Atax 

 ypsilophorvs. 



There is one species of Atax (A. crassipes) very common in some 

 places, of which I have taken large numbers quite free-swimming. 

 Plate 30, (/, will give a good idea of the male. While on the Broads 

 with Mr. Scourfield last August we one day rowed to Sutton 

 Staithe, and as we were tying up the boat previous to landing we 

 saw large quantities of fresh-water sponge (SponyiUa fluviatilis) 

 on the piles supporting the landing-stage. When we returned at 

 night we took as much as we thought fit back with us to the 

 laboratory for examination. Imagine our surprise when we 

 found, on cutting sections through this sponge, that it contained 

 large numbers of A tax crassipes in all stages. There were the 

 egg, larva, nymph, and adult, and all in splendid condition. Atax 

 crassipes is a very common mite on the Broads, but I was so 

 pleased with this find that I was very impatient until I could get 

 a sample of sponge from the East London Waterworks to see if 

 that was affected in the same manner. But I am sorry to say I 

 did not find any trace of Atax crassipes at all — or, in fact, of any 

 other mite. It is only fair to sav, however, that I did not 

 succeed in finding any Atax crassipes free-swimming, so it is very 

 likely that there are none at present in the reservoirs of the East 

 London Waterworks. 



Having completed their parasitic stage the larval mites become 

 nymphs, with eight legs, so that they are practically the same 

 in form as the adults, except in the genital area. AVe have no 

 proof of their being parasitic in this stage, except those that we 

 find living inside the shells of the fresh-water mussels, and these 

 appear to be parasitic in all stages. How long the nymph stage 

 lasts we are at present unable to say, but to all appearance the 

 time in some cases, such as ffydrachna, is twelve months. As 

 they gradually approach the completion of the nymph period of 

 their existence the adult form is being formed inside in a similar 

 manner as we observed the nymph being formed in the larval 

 skin ; but the actual change from nymph to adult is no doubt 



