84 
BRITISH ENTOM OSTRACA. 
according to Straus, from four to six. In winter I have 
found the interval between the eggs being deposited in the 
open space and the young being born to be eight days, as 
may be seen in the experiment detailed above. Moulting 
takes place every time after the young are born ; and 
generally within a very short period after the change has 
taken place, eggs are again deposited. Occasionally, how- 
ever, this does not take place, and then the animal remains 
without eggs for a space of time equal to that of carrying 
the egg s, when she moults again, and then has eggs. 
Straus says, that the young of the same laying are, gene- 
rally speaking, all of one sex, the two sexes being seldom 
found together in the same birth. He also says that the 
Daphniae cease to produce at the approach of winter, and 
to change their skin, and that they die before the com- 
mencement of frost. This does not accord with my ex- 
perience, having found them in considerable numbers, 
producing young and moulting as late as the month of 
December, after both frost and snow had taken place. 
Indeed, I have found them as late in the season as Feb- 
ruary, though not in great numbers ; but about that time 
they seem to disappear, and perhaps in a severe winter 
they perish earlier, as young individuals only are generally 
to be met with in the spring.* 
At particular seasons the Daphniae may be found with 
a dark opaque substance on the back of the shell. This 
is what I have so frequently mentioned above as the 
ephippium, so called by Muller, from the resemblance 
it bears to a saddle. This author was the first who 
took notice of this curious appearance ; but though he 
describes it well, and has given an accurate representation 
of it, he does not give any opinion upon the cause or use 
of the formation. Jurine next noticed it; he describes 
it carefully, traces its gradual formation from matter con- 
tained in the ovary, and states it as his opinion, that it 
* In a mild season they may be found all the winter through ; and even in 
the beginning of March I have found the D. pulex in great abundance and 
of large size, many also with ephippia. 
