April, 1011.] 77 



3-4 mm., was found in the mantle and tlie mantle cavity. Three 

 snails, collected from the sides above the level of the water were 

 also examined, and each contained a larva (see figures below). 



a — foot. b — mantle edge. c — liver. d— intestine. e — head of larva. 



On April 25th I performed the following experiment : "A small 

 larva, 4 mm. long, and a small snail, about 6 mm. were isolated in 

 a jar and brought in contact with one another. The larva imme- 

 diately fastened on to the snail, crawling round and trying most 

 persistently to get under the edge of the mantle, making for the 

 pvilmonary orifice in particular. The snail at once became very 

 lively, twisting its shell about as if trying to rub off the larva 

 against the side of the jar. The larva, however, succeeded in 

 penetrating the pulmonary orifice, and soon was not visible externally 

 (except, being red, it shows through the thin shell). The snail 

 appeared inconvenienced, and soon crawled about two inches out 

 of water, and remained there. An hour later I dropped it to the 

 bottom of the jar. Next morning the snail was in the same place, 

 expanded and dying ; the larva had left it, and had spun a tube 

 close by." 



I repeated this experiment several times, and succeeded often in 

 observing the larva enter the snail. They attacked the small snails 

 more readily than the large ones. A large 9 mm. larva tried to 

 attach itself to a large snail, but unsuccessfully, and then began 

 gathering vegetation around itself and spinning a tube. This larva 

 changed to a pupa about the middle of May (I was absent at the 

 time, so cannot give exact date), and on May 25th I foimd a dead 

 imago on the surface of the water. On April 12th I had foimd 

 two imagines on the water in Trafalgar Square, but injured them 

 so much in the capture as to render them incapable of identification. 

 All I can say is, that the three specimens were green-bodied 

 Chironomids. Neither can I say whether they appear continuously 

 from April, or even March (the two larvae found on March 4th 



G 



