612 
DR. T. WILLIAMS ON THE BLOOD-PROPER AND 
genera, however, the presence of organized cells floating in the nutritive 
fluids indicates an advance in the organic composition of the latter, as compared 
with those of the inferior Echinoderras. Thus the iiiorphous elements of a li\*ing 
fluid become criteria of its zoological status. 
Chylaqueous Fluid of the Echinoderms. — In the economy of all Starfishes the 
chylaqueous fluid is far more voluminous, and enacts a much more important part 
than the blood-proper. The latter system, in the Crinoidea, Asteriadce, and Echinidce, 
bears to the former an insignificant proportion. In the Sipunculidae it has assumed 
a somewhat greater relative development. In the Holothnridan genera it exhibits 
the most advanced condition under which it is known to exist in the Echinodermal 
series. The proportion between these two systems, when they exist together in the 
same individual, is thus shown to be inverse. The fluid contained in the “water- 
vascular” system and peritoneal cavity of the Echinoderms is described both bv 
Tiedemann and Sharpey* as consisting of pure unorganized sea- water. In his Mo- 
nograph on this class, Muller avowedly adopts the same view. Analogy and 
demonstration will now be shown to be opposed to this opinion. 
The peritoneal cavity exists in all Echinoderms. In all species this space is 
occupied by a fluid; in all species, including the Ophiocomidae and Ophiuridae, 
this fluid penetrates through hollow axes, into the arms and lobes, and all the 
membranous processes of the tegumentary system. In all Echinoderms the interior 
of the stomach and its dependent caeca are lined with vibratile epithelium. This fact 
establishes a connection between the Echinoderm and the Medusae, the gastro- 
vascular canals of which were proved to be similarly ciliated, whilst it disjoins them 
in a striking manner from the Entozoa and Annelida, digestive organs of which, as 
will be afterwards proved, are never furnished with vibratile epithelium. The 
boundaries of the peritoneal cavity are universally ciliated. All the integumentarv 
membranous processes are lined within and without with ciliary epithelium, and con- 
sist of hollow prolongations of the peritoneal cavity. In Asterias rubens, the cuta- 
neous membranous processes are readily distended by injection thrown into the 
peritoneal cavity. Thus injected they rise, in relief, to a considerable distance above 
the plane of the integumentary surface. 
They are ccecal at their distal ends. This fact is absolute throughout the Echino- 
dermal families. 
These processes in Asterias are disposed, on the dorsum of each lobe, in four longi- 
tudinal series. They constitute the veritable respiratory organs. They are designed to 
expose to the external, aerating element, not the true-blood, but the chylaqueous 
fluid, the contents of the peritoneal cavity. If this fluid consisted only of pure 
sea-water, what chemical change could result from such an exposure ? No endosmotic 
and exosmotic currents could occur between fluids of identical densities. And where- 
fore that remarkable movement of the corpuscles of the chylaqueous fluids in the 
* Art. “ Echinodermata,” Cyclop. Anat. and Phys. 
