322 H. J, Clark on the animality of Sponges. 
the body. This remarkable feature is scarcely to be recognized 
during the free state of the animal; but when the latter is moored 
transverse diameter coincident with the line of vision. The 
then seems, at first sight, to have a symmetrical aspect, such as 
is not observable from any other point of view; and such it 
might be made to appear if I should belittle the importance of 
one single organ, by simply mentioning its existence, and omit- 
ting to lay down its exact topographical relationship. I refer to 
the contractile vesicle. During the systole of this organ it is so 
inconspicuous that it would easily escape even the most careful 
observation; but during the transition to the expanded state, 
and at the full diastole, its prominence, from the point of view 
just mentioned, is so great as to rival the flagelium in attraction. 
It may then be seen as a comparatively large, rounded, trans- 
parent, vesicular body, which stands out in strong profile, just 
in front of the middle, and close to the-surface of the left side of 
e body. At full diastole it even forces the overlying region 
fo 
side, viz: to show that they are not adult. I think moreover 
that I am fully warranted in assuming that a Monas which 
sesses such an organization as I have described, and is attac 
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