46 
POPULAR SCIENCE REVIEW. 
iron had been mixed with the water, or as if a current of blood 
had flowed into it. 
There are two or three facts connected with the history of 
these water-fleas which are marvellous to our comprehension ; 
and as these animals are easily preserved alive, it is no very 
difficult matter to watch the various processes and witness the 
extraordinary facts with our own eyes. 
The first thing which strikes the investigator into their 
history is the wonderfully prolific nature of the little creatures. 
They give birth to young a great many times during the short 
season of their lives, and some of the larger species have as 
many as forty or fifty eggs and upwards’ in their ovary at once. 
About ten days after birth, the young ones begin to have eggs ! 
and it is probable they continue to produce fresh broods all the 
summer through at frequent intervals. The males (fig. 6) are 
very few in number compared with the females, and it appears 
a well-established fact that, when a female once becomes im- 
pregnated, her fecundity continues for life without any further 
intervention of the male, and this fecundity is transmitted to 
her female descendants for many successive generations. I have, 
by isolating them immediately after birth, proved the fact that 
the young daphnia, born during the early summer, does not 
require the access of the male to become a mother, and have, 
by repeatedly isolating the young as soon as they were born, 
succeeded in following up the successive generations as far as 
the fourth, and Jurine has followed them up as far as the sixth 
without any diminution of their fertility. At particular seasons 
of the year the mature daphnise may be observed to have a 
dark opaque substance on the back of the shell. Muller, who 
first noticed this appearance, for want of a better name, called 
it the ephippium, or saddle, but Strauss has shown that in this 
peculiar-looking substance there are gradually formed two eggs, 
which have been called the winter eggs , and which, at a certain 
period of the animal’s life, are thrown off its back and left to 
float on the surface of the water (figs. 9, 10). In this saddle 
the eggs remain during the winter, protected from the severity 
of the cold, till the spring comes round, when they are hatched 
by the returning warmth of the season. These young daphnise 
are exactly similar in appearance to those produced direct from 
the mother, and, strange to say, are equally independent of any 
access of a male for fecundation. By isolating the young from 
these winter eggs, I have followed up at least four successive 
generations, without seeing any diminution of their prolific 
nature. 
Another very curious fact connected with the history of these 
animals is the regular process which they undergo of moulting , 
or casting their old shell and forming a new one. Though this 
