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 Ploiwma, 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 
T.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 
Chlorophycee only, as these overtop the other plants so greatly. The 
pulse of August 31 occurs a week before the culmination of the 
Chlorophycee is reached, but in the presence of abundant food. The 
dependence of these pulses of Brachtonus 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 
