463 



Note on the Occurrence of Living Hydrachnid Larvae in 



THE Stomach of a Trout. 



By C. D. Soar, F.R.M.S. 



{Ilead Jamiary 16f/i, 1903.) 



On May 11th, 1902, in the course of the investigations carried 

 out by the " Lake Survey " under Sir John Murray, a trout was 

 taken from Loch Kannoch, in the stomach of which Dr. T. N. 

 Johnston found Hving larvae of Hydrachnids. They were very 

 Hvely and in great abundance, and when the contents of the 

 stomach were put into saucers of water, the mites swarmed to the 

 side towards the hght, and were easily caught with the pipette. 

 No dead specimens were seen. Some of these mites were after- 

 wards killed in a preservative solution and kindly forwarded to 

 me through Mr. Scourfield for examination. Permission was also 

 kindly given by Sir John Murray and Dr. Johnston to publish 

 any note on them I thought fit in the pages of our Journal. 



Now it is very well known that nearly all the larvae of water- 

 mites pass one stage of their existence as parasites on some other 

 form of aquatic life. They have been found on insects out of the 

 water, but only on such insects as have passed a part of their 

 lives in an aquatic state, such as gnats, dragon-flies, etc. Severa 

 species of Atax are found in fresh-water mussels. Other mites 

 have been found on Dytiscus, Corixa, Notonecta, Nejxt, Ranatra, 

 and other insects. Carl Thon has found jthem parasitic on fresh 

 water snails. Krendowskij has found the larvae of Arrhenurus 

 on the wings of a dragon-fly. Water-mite larvae have also 

 been found attached to small fish (see note in this Journal, ante, 

 p. 65). But I believe this is the first time that larval forms 

 of a Hydrachnid have been found living in the stomach of 

 a fish. 



I have carefully examined and drawn the larvae, but I am not 



