622 
DR. T. WILLIAMS ON THE BLOOD-PROPER AND 
The Annelida, in a much more marked degree than the Entozoa and Echinodermata, 
are characterized by the possession of two distinct systems of nutrient fluids, of which 
one consists of the pi-oper and true-blood, circulating definitively in perfect and closed 
vessels ; the other, of a liquid mass, filling, in nearly all instances, the peritoneal cavity, 
and corresponding with, as it is the linear continuation of, that which, in the Entozoa 
and Echinoderms, was distinguished as the chylaqueous fluid. In the Annelida this 
peritoneal fluid is charged with corpuscles, which in different genera are sufficiently 
dissimilar to constitute significant generic characters, and these differences are even 
traceable to different species of the same genus. As in other classes, so in the An- 
nelida, upon these two fluids two distinct and separate physiological functions de- 
volve ; each is essential to the maintenance of life. The history of the chylaqueous 
fluid and that of the blood-proper will be studied in this class with more minuteness 
than in the former, for it seems not a little probable that the “ tangle unravelled” by 
the study of these fluid elements of nutrition in the Annelids will conduce to more 
exact views than those now prevalent in physiology with reference to the mechanism 
of nutrition in all invertebrate animals. 
All the recesses and ramifications of the general cavity of the body in the Annelids 
communicate freely with each other, constituting thus one common space. This 
space is lined by a distinct membrane, which is obviously the anatomical analogon of 
the peritoneum, and is filled by a fluid which is unquestionably an organic Jiuid. In 
the Annelida the peritoneal membrane is not vibratile, the oscillations of the fluid 
contents cannot therefore be due to ciliary vibration. This fact distinguishes the 
Annelids from the Echinoderms, Medusae and Zoophytes ; it further proves that the 
movements of the chylaqueous fluid are not in all cases dependent on the presence 
of cilia. The rule is suspended in this class. In Glycera alba, and in one or two 
other species, however, the peritoneum where it penetrates the appendage is lined by 
vibratile cilia. Anteriorly to the researches herein recorded, I am not aware that any 
anatomist has recognised the I’eal physiological meaning, or described the true 
histological characters of the chylaqueous fluid in the Annelida. In the historical 
introduction to this paper I have already indicated the extent to which the researches 
of M. Quatrefages have proceeded in that direction. To him undeniably belongs 
the credit of having independently determined the fact of the existence of ^a fluid’ in 
the visceral cavity of the Annelid. The first publication of his generalized results 
occurs in the Annales des Sciences Naturelles for 1852 . The results of my dissections, 
announcing the existence of a chylaqueous system of fluid in the Annelida, were 
first made public at the Meeting of the British Association, which was held at Swan- 
sea in the year 1849 . It was not until this year ( 1852 ) that I became acquainted 
ence to, the fluids. The light already reflected on the question of their organization, which has so long re- 
mained unanswerable, has rendered the habitats, unusual though they be, affected by these eccentric beings, no 
longer an arcanum, a theme of superstitious wonder, in physiological science. 
