618 
DR. T. WILLIAMS ON THE BLOOD-PROPER AND 
processes, though variously scalloped, into which the Jiuid of the visceral cavity freely 
penetrates. At their bases they are supplied with a few true-blood-vessels. They are 
lined within and without by ciliary epithelium ; in this particular they are not to be 
distinguished from the corresponding organs of those species of Annelida in which 
the chylaqueous fluid alone is submitted to aeration. 
It is important to remember, that, notwithstanding the existence of ‘‘ the respiratory 
tree” for the direct admission of water into the interior of the body, in Holothuria the 
peritoneal cavity, as formerly stated, is filled with a highly corpusculated fluid which 
penetrates the hollow cephalic tentacles, as in Sipunculus, to receive the influence of 
the surrounding medium. In the Sipunculidse the peritoneal cavity is occupied by a 
richly organized fluid profusely charged with corpuscles of peculiar and distinctive 
microscopic characters (see figs. 6 and 7)- The whole interior of the cavity is lined 
with vibratile epithelium, and the motion of cilia prevails over the hollow interior of 
the cephalic tentacles, sustaining in constant and rapid oscillation the corpuscles of 
the chylaqueous fluid, and in these situations ministering directly to the function of 
respiration. As exhibited in the above illustrations, which are strictly faithful to the 
original, the inorphotic elements of the fluid of the peritoneal cavity in the Sipunculidae 
differ remarkably from the corresponding elements in all other Echinoderms. They 
consist, as in part already described, of nearly flattened oblong bodies, inclining to 
the oval, containing a bright, highly refractive and very small nucleus. In some cells 
a second nucleus may be discerned. The parent cells are filled with a fluid which is 
perfectly devoid of granules and molecules. This fluid has an obviously pink or 
faint red tinge. From the contrast between their own colour and that of the fluid 
(opalescent) in which they float, the cells become beautifully conspicuous objects; 
but in the Sipunculidse and Holothuriadse these bodies are so numerous as to impart 
to the fluid, viewed as a whole, a thick, milky pink appearance. The organic 
quality of this fluid in these orders, at all events, it is impossible to doubt ; nor can it 
be disputed for a moment, that the cavity in which it is contained in the Vermigrade 
Echinoderms corresponds, nay, is anatomically identical, with that which holds the 
LESS opake and less organized peritoneal fluids of the Asteriadse, Echinidse, Ophi- 
uridse and Ophiocomidse. In these orders, severally, it is the same fluid, chemically 
and physiologically. In all it occupies the peri-visceral or peritoneal chamber. These 
indisputable facts establish conclusively the view which denominates the peritoneal 
fluid of Asterias, even though it may look like pure water, as a vitally endowed fluid. 
In addition to the bodies above described, which are the proper corpuscles of the 
chylaqueous fluid in Sipunculus Harveii and S. Jolwstoni, others may be observed in 
every specimen and at every season of the year, which severally resemble germ-cells 
and sperm-cells*. 
* I have designedly avoided in the text all discussion as to the real character of these ova- and spermato- 
zoa-like bodies. which are constantly found in the chylaqueous fluid of nearly all zoophytic, radiate and articulated 
animals. In another communication I propose to contribute materials which will probably set the question at 
