153 
noted, but they are rare. The greatest proportion of egg-bearing 
females appears during the rise of the pulse, as is seen in the follow- 
ing table, which gives the data of the vernal pulse in 1898. From 
ANURZA COCHLEARIS. 
No. of ‘ | Ratio of 
Date ovigerous Total Total eggs to No. of 
females females eggs individuals dead 
hoje ne ee pene ae 800 2,200 SOLO) | il BR 0 
soy aS OR a eee i ae 6 , 400 15,200) 8,800') 1: 1,73 400 
PMD Okara ke} eyes 45 ,000 137,800 | 65,000 01 oh Paw 3, 200 
MEO ISTs kak ho oes reine ae 536,000 170224007552 900 40. 1.85 9,600 
Bleciy RUO Ee enter seats tends 489 , 600 1,145,600 | 643,200 | 1:1.78 99,200 
IMMUN WA hrc e ow « 110,400 434,800 | 160,000 | il 3 Qo wil 100,000 
INTE E2 a, ee 6,000 21,200 7,200 12 OF 1,800 
Mii Mod borate yot 8 os 3,000 11,200 Se A007 3h29 1,800 
April 12 to the crest of the pulse on May 10 (not inclusive) the aver- 
age ratio of eggs to individuals was 1 to 1.87. From the crest to the 
foot of the decline inclusive the ratio is 1 to 2.98. The number of 
empty loricze is given below, and it will be noted that on the week 
prior to the crest of the pulse there were 107 living to one dead; on 
the crest itself, one to twelve; while the week following the crest of 
the pulse there was an empty lorica for every 4.3 living females. 
Rapid multiplication thus attends the rise of the pulse and rapid 
destruction its decline. Parasites were very rarely observed 1n this 
species. The decline of a pulse is thus due to the cessation of 
reproduction and a relatively heavy death rate. 
Apstein (96) finds that in Lake Plon Anure@a reaches its maxi- 
mum in July and is at its minimum in April. It is everywhere 
common in the German waters. A. tecta, on the other hand, was 
found only in the smaller lakes and in great numbers, replacing 
cochlearis in warmer months to some extent. Lauterborn (’98) 
regards it as the most abundant rotifer in the Rhine. Our statistical 
records do not show that this is the case in the Illinois, for it is here 
