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 



ANUR^EA COCHLEARIS. 



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 thp 

 foot of the decline inclusive the ratio is 1 to 2.98. The number of 

 empty loricus is given below, and it will be noted that on the week 

 prior to the crest of the pulse there w r ere 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 in 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 Anuraa reaches its maxi- 

 mum in July and is at its minimum in April. It is everywhere 

 common in the German w r aters. 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 



