628 
DR. T. WILLIAMS ON THE BLOOD-PROPER AND 
is elaborately developed. In the larger species the parietes of the feet are embraced 
in a framework of reticulate blood-vessels ; but the interior of these appendages, which 
is hollowed into a cavity, filled with the peritoneal fluid, proves that both systems of 
fluids participate equally in the process of respiration. These worms are the most 
active in their habits of all Annelids, which results probably from the perfection of 
their circulating system. 
In the genus Spio* the chylaqueous fluid is subordinate in amount and import- 
ance. Its corpuscular elements are imperfectly developed. They are opake milky 
globules, possessing sometimes a nucleus, and sometimes none: they are almost 
entirely destitute of granules. In these elegant worms it is the blood-proper system 
that usurps the office of respiration. The branchiae convey into contact with the 
surrounding element very little of the chylaqueous fluid. It is held in the areolae 
of the membranous appendages attached to the branchiae (figs. 28). 
In Nephthys Hombergii, though not conspicuous, the chylaqueous fluid is con- 
siderable in volume. Its motions are limited in consequence of the frequent bridles 
by which the intestines are tied to the integment. Its corpuscles (fig. 30) are rela- 
tively scanty. They are spherical in form, and filled with secondary molecules. The 
oleous globules which accompany them are numerous. The inferior importance of 
the chylaqueous system in these worms is compensated by the highly ev’olved con- 
dition of that of the blood-proper. The branchial processes, which are hollow, are 
filled with a coil of vessels, and with a stream of chylaqueous fluid; both fluids 
therefore in equal proportions are submitted to aeration. 
Of the corpuscles of the peritoneal fluid in the genus Glycera (fig. 31) there is this 
extraordinary fact to be related, that they are blood-red in colour, and not unlike in 
figure and size those of the blood of Reptiles. In this beautiful worm the true-hlood 
conforms with the Annelidan law of perfect fluidity ; it bears no visible elements, and 
is light red in colour, the colouring element, as in all other Annelids, being dissolved 
in the fluid mass. It is remarkable that the Jluid contents of the visceral cavity in 
Glycera should be colourless, while the corpuscles which it holds in suspension 
should be filled with a blood-red liquid, contrasting these bodies in a striking 
manner with the fluid in which they float. The cavity of the peritoneum is dispro- 
portionately capacious. It is little interrupted by segmental septa. The worm is 
extremely quick and active in its movements. The true branchice are hollow cylin- 
drical appendages, lined within and without by vibratile epithelium, and penetrated 
only by the fluid of the peritoneal cavity. They are supplied by no true- blood-vessels. 
The chylaqueous Jluid therefore is the subject of the respiratory change, for tvhich 
these appendages present an appropriate mechanism. 
To this fact the highest interest attaches. It constitutes an undeniable proof that 
the fluid of the peritoneal cavity is capable of discharging the higliest function of the 
animal organism. The presence of red corpuscles in the fluid of this species does 
* Of which three species are found on the coast of Swansea. 
