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be found out about it. No one, for example, has ever had the 
patience to watch the animal from its birth to its death ; to find out 
its ordinary length of life, the time that it takes to reach its full 
growth, the period that elapses between its full growtli and death, 
or, indeed, if there be such a period. And yet even these are 
points which are well worth the settling. For if Melicerta reaches 
its full growth any considerable time before the termination of its 
life, it would seem probable that, owing to the constant action of 
its cilia, it would either raise its tube far above the level of its 
head, or else be constantly engaged in the absurd performance of 
making its pellets and then throwing them away. Who has ever 
found it in such a condition, or seen it so engaged? Yet the 
uninterrupted action of the pellet-cup would turn out the six 
thousand pellets, which form the largest tube that I am acquainted 
with, in about eight days, and those of an average tube in less than 
three, while the animal will live (according to Mr. J. Hood*) nearly 
three months in a zoophyte trough, and no doubt much longer in its 
natural condition. It is true that the creature’s industry, in tube- 
making, is not continuous. It is often shut up inside its tube, when 
all ciliary action ceases ; and, moreover, when expanded, it may be 
seen at times to allow the formed pellet to drift away, instead of 
depositing it : but, allowing for this, there is no little difficulty in 
understanding how it is that, with so vigorous a piece of mechanism 
as the pellet-cup, the tube at all ages, except the earliest, so exactly 
fits the animal. I am aware that it has been stated that the whole of 
the cilia (including those of the pellet-cup) are under the animal’s 
control, and that their action can be stopped, or even reversed, 
at pleasure. But this I think is an error. Illusory appearances, like 
those of a turning cog-wheel, may be produced by viewing the ciliary 
wreath from certain points, and under certain conditions of illumina- 
tion ; and these apparent motions are often reversed, or even stopped, 
by a slight alteration either in the position of the animal, in the 
direction of the light, or in the focussing of the objective. When, 
however, under any circumstances, the cilia themselves are distinctly 
seen, they are invariably found to be simply moving up and down ; 
now lashing sharply towards the base, and now recovering their 
erect position. Even the undoubtedly real reversal of the revolution 
of the pellet in its cup, which is constantly taking place, can be 
easily explained by purely mechanical considerations, and consistently 
with the continuous up and down motion of the cilia. Moreover,"of 
the absolute stoppage of the cilia, in the expanded rotiferon, I have 
never seen a single instance. In all cases, on the slightest opening 
of the corona, the cilia begin to quiver, and they are always in 
full action, even before the disc is quite expanded; while, should 
Mr. Hood, of Dundee, has kept in liis troughs Melicerta ringens for 79 days, 
Limnias ceratophylli for 83 days, Cephalosiphon limnias for 89 days ; the Floscularise 
usually lived about 50 days, but F. Iloodii died, before maturity, in 16 days. 
