197 



ber 1, but is continuously present in the winter of 1898-99 from 

 December 6 till March 28, when collections ceased. 



Male eggs were recorded but once April, 29, 1895 and there 

 is no other evidence of the cycles of reproduction beyond the pulses 

 in numbers. They suggest a polycyclic habit with major pulses 

 in spring and fall. It is apparent that conditions affect these cycles 

 greatly, as is seen, for example, in the contrast between the earlier 

 years, with low water in the spring, and the later ones, when high 

 water was longer continued. 



This variety, rubens, has not been widely reported in the plank- 

 ton. Skorikow ( '96) finds it in June in the River Udy, and Kertesz 

 ( '94) reports it from Budapest, while Stenroos ( '98) finds it in the 

 littoral fauna of Lake Nurmijarvi in Finland, and also in the plank- 

 ton in July and August. 



Brackionus urceolaris var. bursarius Barrois and v. Daday. 

 Average number of individuals, 206; of eggs, 33. This is a sum- 

 mer variety, and forms but a small part less than one per cent. 

 of the total number of individuals referred to the species. 



Brachionus variabilis Hempel. This species was found but once 

 in 1898, but was more abundant in former years (see table on oppo- 

 site page). The largest development which it attained in the Illinois 

 was a pulse of 168,222 on August 15, 1894, at 84. The largest 

 number in subsequent years was 5,200 per m. 3 on August 8, 1896. 

 It may be significant of the connection of this form with the urceo- 

 laris-rubens group that the great pulse of 1894 was coincident with 

 an unusual development of rubens on that date. 



This species is a summer form, the earliest record being May 24, 

 1898, at 74, and the latest September 25, 1895, at 73. Its opti- 

 mum temperatures lie near the summer maximum. If this form 

 should prove to be merely a spinous variety of B. urceolaris it will 

 afford another illustration of spinous varieties of Brachionus appear- 

 ing at high temperatures, in accordance with the hypothesis of 

 Wesenberg-Lund ('00). 



In Table I. there is given for 1898 the seasonal distribution of 

 the free winter eggs of Brachionus. It will be seen that they occur 

 throughout practically the whole year, with some increase after the 

 times of the April-May and September pulses. 



Cathy pna leontina Turner. Average number, 47, in 1896, a year 

 of disturbed hydrograph ; less abundant in previous years, and not 



