DR. T. WILLIAMS ON THE HLOOD-PROPER AND 
f.04 
The presence of cilia on the internal surface of these canals strikingly and funda- 
mentally distinguishes the latter from true blood-vessels, and intimately allies them, 
homologically, with the spacious perigastric chambers of the Echinoderins and 
Annelids. 
The fluid contained in the gastro- vascular canals of the Medusm is a compound of 
salt water and chyle. In the Rhizostomidse it presents a yellowish hue, in Velella it 
is bluish ; it is always corpusculated. The floating cells exhibit great irritability, but 
they are not locomotive; the minute molecules are mutually repulsiv^e. In this fluid 
living polygastric animalcules are constantly met with. The fact of their constant pre- 
sence proves the direct admission of the external sea-w^ater into these canals, but they 
are in time digested. The largest corpuscles are furnished with an involucrum, tig. 3. 
In Rhizostoma (a specimen of average size) they vary in measurement from xwo^th to 
-g^g^jdth of an inch. They are never organized to such a standard as to contain a 
defined centric nucleus. 
The formative power of the cell is expended in the production of secondary oleagi- 
nous cellules and ‘ molecular base,’ which constitute the contained parts of all the 
larger parent-corpuscles. The smallest cells are filled only with a limpid oleine, of slight 
refractive power. Evaporated, in Rhizostoma this fluid yields abundant crystals of 
chloride of sodium. In no Acaleph whatever are the gastro-vascular canals tunnelled 
in the centre of the substance of the disc. They are always situated as superficially 
as possible on the inferior surface of the disc in the Pulmograde Medusae ; in the 
Ciliograde under the external cuticle of the globe in immediate relation with the 
cilia. In this anatomical arrangement the physiologist discerns a true intention, that 
of exposing the fluid contents to the aerating agency of the surrounding medium. In 
Rhizostoma the yellow colour has its seat in the fluid, not in the floating cells. It is 
a fact of singular interest, that the corpuscles of the chylaqueous fluid in this, as in 
ALL other classes in which it exists, vary in size with the variations in the size of the 
body of the individual specimen under examination. In this respect they are diame- 
trically distinguished from the morphotic elements of the true-hlood in vertebrated 
animals, the corpuscles of which bear no proportion in size to that of the body of the 
animal from which they are taken. This general observation wdll be afterwards con- 
firmed by a variety of particular exemplifications. It has now been shown that in 
Zoophytes and Medusae sea-water is admitted in large quantities, more or less directly, 
into the chylechannels, with the contents of which it more or less directly mixes and 
vitally assimilates. This fact may at present be mentioned as another fundamental par- 
ticular, in which the chylaqueous fluid, in all animals, is distinguished from the blood- 
proper, for into this latter fluid the external element is never immediately admitted ; 
it is previously subjected to the influence of one or more organic processes ; it is thus 
Mr. Huxley had recognised the principle that in all Acalephce the interior lining of the stomach and gastro- 
vascular canals was more or less generally ciliated, that the movements of the fluid contents were in great part 
due to the agency of cilia. 
