82 
BRITISH ENTOMOSTRACA. 
number, but as yet no trace of any part of the body is 
recognisable. A little afterwards we see a black spot in 
the centre, which is the eye, and is the first organ visible. 
The other organs then begin to show themselves, but it is 
not till near the end of the fourth day, or ninety hours 
after laying, that motion is perceptible. At the end of 
the fifth day the young are launched into open day. They 
are from the first exactly like the parent, undergoing no 
metamorphosis, but merely differing in the less complete 
development of parts. In the case of the D. pulex, the 
young are born with the prolonged spine at the extremity 
of the valves curled up within the shell ; and very shortly 
after birth, a few seconds after they have begun to move 
about in the w T ater, this tail may be seen to spring forth 
with a sudden jerk, and assume its natural position. The 
setae of the large antennae or rami may also be seen to 
spring out in the same sudden manner, having been appa- 
rently folded up along the stem. During the time this 
process is going on, the little creature may be seen fre- 
quently 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 large antennae are bent 
downwards, so as to enter the interior of the shell, where 
they are embraced by the feet, and quickly drawn through 
them, so as to catch the ends of the setae, and raise them 
up. At this time the motions of the animal are exactly 
like those of the common house-fly, when it stops to clean 
its wings and feet. This sudden evolution of these parts 
is attempted to be accounted for by Straus, from the in- 
stantaneous flow of blood into these organs. In a very 
short time after birth the young animal is exactly like the 
parent, and gradually increases in size, till the shell be- 
comes too small to hold it, when it throws it off, and 
comes forth with a new and a larger one. 
This process of moulting is very curious, and all-im- 
portant for the life of the animal. The intervals between 
them vary according to the season of the year, being 
shorter in summer than in cold weather. Schoeffer says 
