650 
DR. T. WILLIAMS ON THE BLOOD-PROPER AND 
there exists but one system of fluids, appearing as if the central stomach of the 
Acaleph had been suddenly partitioned from its dependent caecal prolongations. 
Viewed from the novel vantage point afforded by the fluids, the mind is led to con- 
template the whole invertebrate kingdom under the guidance of three leading ideas ; 
— 1st. It sees in the Zoophytes a group of animals in which the fluids form a single 
system in free communication with the external element. Advancing to the limit of the 
Echinoderrn, it suddenly descries the superaddition of a totally distinct system, that, 
namely, of the true-blood, while the former still persists ; it tracks this double fluid- 
chain up to the highest articulated animal ; and, Srdly, at the highest frontier line, 
hounding the Medusae, it observes a divarication in the chain, by the divergence 
from the originally single portion of the molluscan branch. In the Mollusca, like the 
Protozoa, the fluids constitute a single system ; but the system of the circulating fluids 
in the former is distinguished from that in the latter by this important fact, that be- 
tween it and the external element there exists no direct communication as in the 
Protozoa. In the Protozoa the nutrient fluids are chylaqueous, in the Mollusca they 
are true-hlood, moving in a closed circle, not of cylindrical vessels, however, and ex- 
cluded from all direct relation with the surrounding element; that is, before salt 
water, in this class, is admitted into the blood, it must, by the laws of this system, 
have first received an incipient organization, by passage through the stomach. The 
assimilating power of the chylaqueous fluid, therefore, as it exists in the Protozoa 
and Echinoderms and Annelida, when exerted upon salt water, immediately converts 
the latter into a vital organized fluid. This power is not possessed by true-blood. 
Classified in accordance with the principles established by the foregoing history of 
the comparative anatomy of the fluid elements of nutrition, the diagram here pre- 
sented (Plate XXXV.) would illustrate the arrangement of the invertebrated classes. 
Swansea, December 12, 1851. 
Explanation of Plates. 
All the following illustrations were examined under and drawn by a one-fourth 
and a one-eighth power of one of Powell and Lealand’s best microscopes. 
PLATE XXXI. 
Fig. 1. Corpuscles floating in the chylaqueous fluid of Tuhularia indivisa. Magni- 
fied 320 diameters. 
Fig. 2, Corpuscles floating in the chylaqueous fluid of Bowerhanhia de7iea. Mag- 
nified 320 diameters. 
Fig. 3. Corpuscles floating in the chylaqueous fluid of the gastro-vascular canals of 
Rhizostoma. Magnified 300 diameters. 
