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XXIII. On the Blood-Proper and Ckylaqueous Fluid of Invertebrate Animals. 
By Thomas Williams, M.D. Land., Extra Licentiate of the Royal College 
of Physicians, and formerly Demonstrator on Structural Anatomy at Guys 
Hospital. Communicated by Thomas Bell, Sec. R.S. 
Received December 18, 1851, — Read March 18, 1852. 
In the following memoir, I propose to submit to the Royal Society a collection of 
facts observed with repeated and scrupulous care, which I trust will suffice to 
establish the propositions, viz, that in invertebrate animals there exist two distinct 
nutritious fluids, dissimilar in their anatomical relations, and different in their 
chemical and vital compositions ; that, in the animal series, a gradation from the 
simple to the complex is observed in the fluid as well as in the solid elements of the 
organism ; that these twm constituent parts of the animal body bear towards each 
other, whether in simplicity or complexity, a constant and direct proportion; that 
the true blood-system does not begin at the beginning of the animal series, but that it 
arises out of {what in this memoir will be called) the chylaqueous fluid, of which the 
blood-proper is the perfected evolution; that the chylaqueous fluid is as much less 
vitalized than the true-blood, as the solid structures of the animals in which the 
former exists are less complex than the analogous parts of those in which the latter 
is found ; that the containing system of the blood-proper is distinguished, with the 
single exception of that of the Echinodermata, by the absence of vibratile cilia from 
its internal lining membrane, while that of the chylaqueous fluid is provided in the 
same situations, almost invariably, with these motive organules ; that the contents 
of the former system are propelled by the contractile force of its muscular parietes, 
while those of the latter are circulated chiefly by ciliary vibration ; that below the 
Echinodermata the blood-proper is wholly supplanted by the chylaqueous fluid ; 
that above the Annelida the latter fluid in the adult animal is superseded by the 
true-blood ; that in the Echinoderms and Annelids these two systems of nutrient 
fluids co-exist, bearing always to each other, in the same individual, an inverse 
quantitative proportion ; that in the Mollusca these two are united into a single 
system, in which the essential characteristics of both are legible ; and that these 
facts, hitherto unrecognised in their physiological connection, and unappreciated in 
their separate meaning, are calculated to elucidate, with new clearness, the processes 
of digestion, sanguification, and respiration, more especially in the lowest classes of 
invertebrate animals ; and finally, that they suggest inquiry from novel points of 
view, into several important questions in zoo-chemistry. 
MDCCCLII. 4 H 
