BRITISH EXTOMOSTRAC A. 



mini her, 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 dav, or ninety hours 



t/ ' V 



after laying, that motion is perceptible. At the end of 

 the fifth day the young arc 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 I). /Wr,r, 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 water, 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 tlie 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 verv 

 short tune afterbirth 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 ne\v and a larger one. 



This process of moulting is very curious, and all-im- 

 portant for the life of the animal. The intervals bet ween 

 them vary according to the season of the vear, being 

 shorter in summer than in cold weather. Schccffer says 



