172 
Brachionus bakert O. F. Mull., type form.—Average number, 2. 
As shown in table on p. 193 (MS.), this form is much more abundant 
in previous years though it is relatively rare, ranking sixth in the list 
of seven forms recognized. The most of the records fall prior to the 
middle of August, and it seems to be an early rather than a late 
summer form. 
Brachwonus bakert var. obesus Barrois and v. Daday.—Average 
number of females, 41; of eggs, 62. The proportion of egg-bearing 
to non-egg-bearing females—2 to 3 in all records—is larger than in | 
any other variety. It seems probable that the lateral expansion 
which marks this variety may be only the result of rapid reproduc- 
tion. In common with most of the other varieties this one occurs 
at the time of the pulses, but it is last in the list of seven, and the 
numbers are too small to trace its seasonal preferences with cer- 
tainty. 
Brachionus bakert var. bidentatus Anderson (non Kertész).— 
Found once—August 5, 1895, at 78°. 
Brachionus bakert var. cluniorbicularts Skor.—Average number 
of females, 90; of eggs, 95. This also was more abundant in all 
previous years. This variety is, next to tuberculus, the most 
abundant of the varieties in our plankton. The two stand at 
opposite extremes of the series of varieties, the former being least 
modified, and the latter most, especially in the direction of asym- 
metry. It includes about one third of all the individuals of the 
species. The ratio in the grand total of females to eggs carried— 
11,708 to 5,976—is somewhat less than the average in the entire 
species. This variety is distributed throughout the whole seasonal 
range of the species with no marked predominance in any particular 
part of it. Itis wholly absent in the early summer of 1897, but very 
abundant in late summer of that year, though not in other years. 
The autumn of 1897 was one of long-continued high temperatures 
(Pt. I., Pl. XI.), and under those conditions this variety constituted 
two thirds of the individuals belonging to the species. If we add to 
it the representatives of rhenanus, obesus, and brevispinus we have 
a total of 15,400 individuals with no posterior spines, or with spines 
but slightly developed, in contrast with only 2,200 with such well- 
developed spines referred to varieties melhemi and tuberculus. The 
conditions of temperature were those in which according to the 
