20 U. S. BUREAU OF FISHERIES. 



two Culex larvae. Throughout the remainder of the summer breed- 

 ing here remained at the same low point, and this was true on the 

 author's visit in August, 1920. 



J 4 (figs. 4, 5) is at the side of the same bay, about 20 yards from 

 J 6. Many loose rocks are tumbled about on the shore here, and 

 among them are numerous pockets into which the water seeps, form- 

 ing little pools quite cut off from direct communication with the lake 

 waters. The brook previously mentioned flows past this shore, car- 

 rying clean water 18 inches to 2 feet deep up to the very rocks 

 that bound the outermost of these pools. Large numbers of small 

 fishes, chiefly schools of young sunfishes, roach, and minnows, are 

 constantly swimming along this shore, and mvid minnows may always 

 be seined. Many of these pools are separated from the lake waters by 

 single rocks a foot or less across, yet are quite shut off from access 

 to the fishes which come to the outer side of the barrier. 



On July 11 and 12 this place was thoroughly studied and a 

 number of the pools selected and marked for various experiments. 

 Others were filled with earth by the laborers. Those pools nearest to 

 the lake usually supported a good growth of Lemna and filamentous 

 algge and abounded in diatoms, desmids, rhizopods, ciliates, and 

 other microscopic life, together with many entomostracans, minute 

 oligochaetes, and a few amphipods, aquatic insects and their larvse, 

 leeches, etc. To tlie hand the water seemed warmer than the circu- 

 lating water of the lake but was always clean and pure. In all of 

 these pools mosquito breeding was very dense, while in the lake only 

 a foot or two removed there was little or no breeding except where 

 obstructions of driftwood or vegetation had accumulated. 



Selecting for further discussion one of these pools about 2 feet 

 in diameter (fig. 4) and another immediately contiguous one about 

 14 inches in diameter for a check, both of which were separated from 

 the lake water by not over 15 inches of rock, the mosquito count 

 gave numbers running from 20 to upward of 50 larvse of Culex 

 fifiens and Aeden sylvestris for each sample. As many were newly 

 hatched the actual number present probably exceeded the counts. 

 In addition there were some egg boats and pupje and an occasional 

 Anopheles larva. Thorough exploration with a small dip net failed 

 to disclose the presence of any fishes in the pools. 



On July 12 mud minnows (Tahle 2, No. 2386, p. 16) seined in the 

 lake at this point contained no mosquitoes but various insect larvse, 

 gastropods, entomostracans and isopods, diatoms, desmids, Confervse, 

 and silt. At the same time by removing a single stone an opening 

 6 or 7 inches wide was made into the larger pool, no change being 

 made in the smaller one. 



On July 15 a single small mud minnow (Table 2, No. 2354) was 

 taken from the opened pool. Its stomach contained two full-grown 

 culicine larvse and two other insect larvse. On this date there was 

 little if any diminution in breeding (average 36 per sami:)le). 



The opening was enlarged and made more direct. On July 24 

 great numbers of young sunfish Avere swimming in schools along 

 the shore, and a number of these, together with three mud minnows, 

 were taken from the pool. In the latter (Table 2, No. 2357a) in a 

 mass of mucli fragmented material were many body hairs, siphon 

 combs, and mouth brushes of larval Culex, some Cyclops, debris, 



