164 



Brachionus pala var. amphiceros Ehrbg. 

 " dorcas Gosse 



" forma spinosus Wierz. 

 quadratus Rousselet 

 urceolans Ehrbg. 



var. rubens. Ehrbg. 



" bursarius Barrois and v. Daday 

 variabilis Hempel 



Brachionus angularis Gosse. Average number of females, 

 57,890; of males, 25; of summer eggs carried, 29,560; of winter 

 eggs, 1,223 ; of male eggs, 54. Of the individuals, 13,973 belong to 

 var. bidens and 43,942 to the type; of the eggs, 2,035 belong to the 

 variety and 28,802 to the type. 



The combined statistics of the species will be discussed before 

 the type and variety receive separate treatment. This species was 

 found in every month of the year and throughout the whole range 

 of temperatures, but the period of continuous presence and large 

 numbers lies definitely between May 1 and November 1 and above 

 60. In fact, in 1898, 98.6 per cent, of all the individuals were found 

 between May 31 and October 4 and above 70. Approximately the 

 same conditions are found in previous years save in 1896, when an 

 earlier spring (cf. PL X. and XII., Pt. I.) is attended by an earlier 

 appearance of this species. Temperature seems thus to have a very 

 decided effect upon the seasonal distribution of the species, and may 

 have something to do with its apparent absence in the cooler waters 

 of our Great Lakes and of L. St. Clair, for in spite of all the work 

 done upon rotifers in those regions by Jennings it has been found but 

 once by Kellicott ('97) in a cove at Sandusky. This identification 

 may be questionable, since he says " I at first took it for B. mollis 

 Hempel." Notops pelagicus, since described by Jennings ('00), is 

 found in the plankton of Lake Erie, and according to him this 

 species is much like B. mollis in its appearance. In any event B. 

 angularis is very abundant in our warm waters and practically 

 absent in the more northerly waters of Michigan, whose summer 

 temperatures are 10-15 below that of the Illinois River and its 

 backwaters. 



Brachionus angularis presents the usual phenomenon of recurrent 

 pulses, but in spite of the large numbers they are rather less regular 



