80 THE AQUARIAN NATURALIST. 



shuttle-shape, with an orifice in the centre ; the ends 

 of the shuttle were more prolonged in others, and 

 several showed obvious indications of four incipient 

 arms in unequal progress around a central orifice 

 (PL I. fig. 4, c). 



On the following day, August 28th, a remarkable 

 change had ensued. The metamorphosis was rapidly 

 advancing, for the elongated arms promised to be of 

 a peculiar tentacular texture (PL I. fig. 4, d). 



In three days longer this tentacular appearance was 

 amply realized the extent of the arms equalled 

 some diameters of the body, the two from the ends of 

 the shuttle remaining always more prolonged than the 

 others. 



All this was an extraordinary exhibition in the off- 

 spring of such parents that so lately issued in the form 

 of almost invisible dust from compact, massy, pon- 

 derous animals, alike remote from their progeny in 

 habits, in form, and in substance. But Nature had 

 an important purpose to fulfil : the apparently rude 

 commencement had to be carried through by wonder- 

 ful expedients to symmetrical perfection in the end. 

 In eleven or twelve days after the simple active atom, 

 the Planula, had been discharged from the unwieldy 

 Medusa, it was converted into a stationary Hydra* \ 

 (PL I. fig. 4, e,f). 



* Unless in very favourable positions, it is by no means easy 

 to follow the history of such minute specks as those of which 

 we treat. The most convenient method of observation is when 

 they are affixed to watch-glasses. The progeny of the Medusae 

 while yet Planulae should be transferred to a flat vessel some 

 inches in diameter, filled to any height with water. One or more 



