185 



The pulses recorded in the table will be found to coincide (Table 

 I.) with those of other species of the genus, and in the main with 

 those of the total Ploima, thus indicating that this species responds, 

 along with other rotifers, to some common factor of their environ- 

 ment. The relation of these pulses to those of the chlorophyll- 

 bearing organisms (PI. I. and II.) is also striking. Of the 30 pulses 

 recorded in the table, 6 fall outside of the period included in Plates 

 I. and II. Of the remaining 24 there are 17 whose culminations in 

 the main coincide with those of the organisms upon which they feed, 

 and 5 of the 6 remaining follow shortly thereafter, usually at the 

 next collection, at an interval of a week or thereabouts. In one 

 case only is there a delay of a fortnight after all of the plant pulses. 

 The large pulses of August-October, 1897, were judged by the 

 ChlorophycecB only, as these overtop the other plants so greatly. The 

 pulse of August 31 occurs a week before the culmination of the 

 Chlorophycecz is reached, but in the presence of abundant food. The 

 dependence of these pulses of Brachionus pala upon the food supply 

 is plainly suggested by their time relations with the pulses in the 

 -plant life of the plankton. 



Further reason for concluding that the species is polycyclic is 

 found in the evidences of sexual reproduction, which will be noted 

 in connection with the discussion of the varieties. In this connec- 

 tion it will suffice to say that there is some evidence that the pulses 

 are preceded by rapid parthenogenetic reproduction, and accom- 

 panied or followed by the appearance of male eggs, males, and 

 winter eggs. 



The eggs of Brachionus pala are detached from the parent in 

 such a large proportion of the cases in preserved material that the 

 tracing of the reproductive cycle by means of attached eggs is ren- 

 dered difficult if not impossible. Furthermore, eggs resembling 

 the winter eggs of this species, and provisionally referred to it in our 

 records, are to be found in the plankton at nearly all seasons of the 

 year, and it is obviously impossible to determine the time at which 

 they were produced. It seems probable that all of the varieties 

 pass through recurrent cycles, and that none of them is a temporary 

 phase of the cycle. 



Outbreaks of parasitic diseases in this species are very common. 

 They almost always attend the larger pulses, but isolated individuals 

 infested by some of these pests are not infrequent, especially during 



