NOTES ON FRESHWATER ENTOMOSTRACA 169 
gave birth to young on 8th February (of. czt., p. 81). Now 
if in the first series of observations we exclude the ephippial 
egg thrown off on 30th November, and reckon from 4th 
December when the normal eggs were first observed, we find 
that this Daphnia had seven broods of young in 67 days; or, 
reckoning from 8th December, when the first brood of young 
ones were born, and not counting that brood, then there were 
six broods in 62 days, or an average of about 10 days 
between each brood. It must be remembered also that 
these experiments were carried on during mid-winter, when 
the productiveness of the little creatures, even though arti- 
ficial heat may have been used, would naturally be less than 
during the genial weather of the summer and autumn 
months. | 
If the ten specimens first referred to be now considered, 
and taking for granted that they would have proved to be as 
prolific as those described by Dr. Baird, and also allowing 
on an average twenty young to each brood for each of them, 
they would in the seven broods have given birth to 1400 
young Daphnia; and, moreover, when we take into con- 
sideration that the young at certain seasons consist only of 
females, and that the young females, according to Jurine, 
begin to produce eggs in about 10 days after birth, and in 
winter, as Dr. Baird has shown, they produce young in 20 
or 21 days after birth, it is not difficult to imagine in how 
short a time a loch will become replenished with a numerous 
fauna. As a matter of fact, if the ten specimens already 
referred to and their offspring were as fertile as the examples 
cited, and taking for granted that all or most of their young 
ones were females, which at certain seasons of the year is 
not unusual among some of the entomostraca, as shown by 
Dr. Baird, our ten specimens of Daphnia pulex would in the 
course of a little over two months have become the progenitors 
of several millions of descendants. 
The following table shows the actual increase in numbers 
of Daphnia in 80 days, beginning with the first brood of the 
10 Daphnize referred to, and allowing 20 young ones to each 
brood, and presuming that these young will themselves 
reproduce 20 days after birth—all the young being 
females :— 
