84 BRITISH ENTOMOSTRACA. 



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 eggs, 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 

 Daphnia3 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 Daphnise 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 Miiller, 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 lias given an accurate representation 

 of it, he does not give any opinion upon the cause or use 

 of the formation. Juriiu- 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 



* Tn a mikl season they may lie found all the winter through ; and even in 

 the lieginnmg <>f March I have found the D. }>//le.r in great abundance and 

 of large size, many also with ephippia. 



