14- life, in its lower forjis. 
marked ( d ). As the two divisions become more separate, 
each assumes an oval form, united at length to its fellow 
only at the base ( e ). At this time the motion of the cilia 
is plainly visible, forming a circle in each within the 
body, near the summit. As the process goes on, the con- 
nexion betwoou the two is reduced to a mere point, aud 
they become capable of separate motion, so far as to 
diverge and look iu opposite directions; the point of 
union being the common stem (/). At this stage we 
may observe that the bell which is destined to remain is 
open at the top, within which the ciliary waves are chas- 
ing each other in continuous wheels, the other bell being 
closed at tho summit. 
But on the latter, which is ultimately to be thrown off 
a new and highly interesting phenomenon appears. The 
cilia, which before the division had played around the 
mouth, have become obliterated, probably by absorption ; 
the orifice at that extremity has closed up permanently, 
for this is to be the base of the new animal ; and a new 
bell-mouth and a new wheel of cilia, are to be formed at 
the opposite end, which at present remains attached to the 
common stem. The first indication we can detect of this 
new formation is a very slight motion in the water, a little 
quivering around what wc must as yet call the basal 
part. Presently there appear waved hairs, which seem 
very flexible, and tho motion of which resembles that of a 
fringe of loose silk moved through water, an action very 
different from the regular waves of perfect cilia. These 
waving hairs increase rapidly in length, and in the vigour 
and rapidity of their undulations, which gradually become 
decidedly rotatory, producing at length strong currents in 
' 
