NOTES ON FRESHWATER ENTOMOSTRACA 169 



gave birth to young on 8th February (pp. cit n p. 8 I ). Now 

 if in the first series of observations we exclude the ephippial 

 egg thrown off on 3Oth 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 2 I 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 DapJmia 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 Daphniae 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 : 



15 D 



