172 



Brachionus bakeri O. F. Mull., type form. Average number, 2. 

 As shown in table on p. 1 93 (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. 



Brachionus bakeri 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 bakeri var. bidentatus Anderson (non Kertesz). 

 Found once August 5, 1895, at 78. 



Brachionus bakeri var. cluniorbicularis Skor. Average number 

 of females, 90; of eggs, 95. This also was more abundant in all 

 previous years. This variety is, next to tuber culus, 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. It is wholly absent in the early summer of 1 897 , 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 XL), 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 



