128 ILLINOIS ACADEMY OF SCIENCE. 



Microdrilse 



Mollusca Ancylus tardus (Say) 



Mosquito Culex sp. adult 



Culex sp. larvae 



Oligochaetse 



Ostracoda 



Paramoecium 



Physidae Physa gyrina (Say) 



Hydrochinidse 



Salamander Amblystoma tigrinum (Green) 



Sphseridae Musculium securis (Prime) 



Musculium truncatum (Lins.) 



Spiders Pilaeus militaris (Hentz) 



Chibonia sp ? 



Sponge Spongilla fragilis (Leidy) * 



Thysanura * 



Vorticelli • • • _• 



Water boatmen Corixa sp 



Water striders Gerris marginatus (Say) 



Water scorpion Ranatra fusca (P. B.) 



Hydrometri martini (Kirk) 



Zaitha 



Totals 5 24 23 25 40 56 64 25 19 15 



As would be expected, the number of species present is greatest 

 in mid-summer. The cuhnination in number of forms living in 

 the water comes in July. The greatest invasion of land forms 

 into the pond area occurs in August when the water level is low 

 and the pond is more nearly choked with vegetation. 



QUANTITATIVE SUCCESSION. 



Qualitative work, however, is not sufficient ground on which to 

 base exact conclusions. It is also necessary to have exact data 

 regarding the abundance of each of these species throughout the 

 year. In order to obtain this information quantitative collections 

 must be taken. The quantitative work carried on so far has been 

 done by means of nets of a known size operated through like dis- 

 tances in as nearly like conditions as possible. It may be added 

 that in order to do away with the obvious sources of error arising 

 from collecting with nets, a galvanized iron cylinder should be 

 used. This should be sunk into the mud for each collection and 

 the animals contained in it counted and their position noted. 



Table II shows the results of quantitative tow-net collections 

 made at the surface of the lilypad region. In these the net used 

 was of millers' bolting cloth, with an opening one foot in diameter. 

 The net was slowly hauled a distance of forty feet with the top 

 of the opening at the water's surface. The collections were made 

 in the early morning or late afternoon to guard against errors due 

 to the daily vertical migration, which was very pronounced. In all 

 instances the figures show the result of one typical haul taken 

 near the close of the month. Unfortunately, the collections for 

 July were made under too diverse conditions to be comparable to 



