408 History of British Entomostraca. 



young are ushered forth into the world, with the tail curved up 

 within the shell ; and very shortly after birth, (Straus says previous 

 to birth, but SchoefFer says a few moments after, which agrees with 

 my own observation,) this tail may be seen to spring forth with 

 a sudden jerk and assume its natural position. The setae of the rami 

 also may be seen to spring out in the same sudden manner, having 

 been apparently folded up along the stem. The suddenness of this 

 motion is attempted to be accounted for by Straus, from the instanta- 

 neous flow of blood into these organs, but it is evident that this 

 rapid evolution of these parts is in a great measure owing to 

 the insect frequently stopping in its career through the water, 

 bending up its body within the shell, and pushing it quickly out 

 again beyond its edges, while the rami are bent downwards, so as 

 to enter the interior of the shell, where they are embraced by the 

 feet of the insect, and quickly drawn through them so as to catch 

 the ends of the setae and raise them up. The motions of the insect 

 during this process are exactly like those of the common house fly, 

 when it stops to clean its wings and feet. In a very short time 

 after birth, the insect is exactly like the parent, and gradually in- 

 creases in size, till the shell becomes too small to hold it, when it 

 throws it oiF, and comes forth with a new and a larger one. This 

 process of moulting is a very curious one, and all important for the 

 life of the animal. The intervals between each vary according to 

 the season of the year, being shorter in summer than in cold wea- 

 ther. SchoefFer says, in the young it takes place every two days, 

 which agrees very nearly with Jurine's experiments performed in 

 the month of June. In winter the intervals are somewhat greater. 

 In the month of December I found them thus: December 8th, 

 young one born. 12th, moulted first time. 14th, moulted second time. 

 17th, moulted third time. 21st, moulted fourth time, and has eggs. 

 29th, moulted fifth time. January 9th, moulted sixth time. 19th, 

 moulted seventh time. In a young D.pulex born from anephippial 

 egg, the intervals were as follows : December 5th, young one born. 

 13th, moulted first time. 17th, moulted second time. 24th, moulted 

 third time. January 3d, moulted fourth time, and has eggs. 11th, 

 moulted fifth time. 18th, moulted sixth time. Each time it moults 

 the insect increases in size, the moulting being evidently, as in the 

 Cyprides, necessary for the gradual growth of the animal. The 

 process does not seem to stop, however, when the insect has acquired 

 its full growth, but, as far as I have been able to judge, continues 

 during its whole life, even long after it has gained its full size. 

 As in the case of the Cyprides, the shell of the Daphinae soon be- 



