XVI u 
INTRODITCTTON. 
averaging *0005 incli, but some attaining *0003. These 
are very numerous in the mass. 
5. Circulatory and Bespiratory systems. These exist in so 
simple a condition that we can scarcely separate them in 
our investigations. Ur. Williams has distinguished by the 
term Ghylagueous fluids “ that fluid which occupies the 
gastric and perigastric cavities of all animals below the 
Annelida.”* It is far less vitalized than true blood, but 
still it is not mere water, being impregnated with organized 
corpuscles and slightly albuminized. In the animals of 
the class before us there is no blood, and no vascular system, 
but the cavity of the body is ample, and is copiously 
occupied by a transparent fluid, which has by some been 
mistaken for sea-water. I have, however, proved by ex- 
periments, recorded elsewhere,t on numerous species, that 
this fluid is copiously provided with organic corpuscles, 
circular or ovate disks, granulose in character, of a clear 
yellow colour, varying from *0001 to "0008 inch in diameter, 
the larger ones inclosing oil-globules. The fluid coagulates 
on the addition of nitric acid, showing that it holds albu- 
men in solution. 
It would appear that the action of the stomach is confined 
to the solution and extraction of albumen and oil, which 
are carried with sea-water into the general cavity, the com- 
pound being a chylaqueous fluid ; and that it is in the 
upper part of the interseptal chambers that it is acted upon 
by the biliary seeretion. 
For the free circulation of this fluid to every part of the 
interior, the whole body is lined with a delicate, strongly 
ciliated epithelium. The ciliary current is upward : when 
a pellucid diantlius has its fosse much exposed, it is quite 
easy to see the current driving up from every part of the 
interior along the whole inner wall, and passing into the 
tentacles, up which the atoms are then hurled. I believe 
there is no change in the set of this cun-ent : for though 
atoms are seen, especially at the bottom of the tentacles, 
occasionally to pass annularly or diagonally ; and though 
of course there must be a return of the fluid driven up- 
ward — for there does not appear, with the closest watching, 
a trace of exit at the tip of the tentacles; and though, 
indeed, atoms are seen, though rarely, to pass downward, — 
I think these irregular and retrograde movements are 
* Phil. Trans. 1852. t Annals of Nat. Hist.; March, 1858. 
