CHYLAQUEOUS FLUID OF INVERTEBRATE ANIMALS. 
629 
not prove that in no other species is this fluid capable of enacting a true respiratory 
function, since the branchial organs of nearly all Annelids (many by it exclusively) 
are more or less injected by the fluid of the visceral cavity. On the other hand, a fluid 
which is destitute of corpuscles may also perform the office of respiration. Floating 
cells are not therefore essential to this process. In Glycera alba (fig. 31) the red 
corpuscles are almost uniformly oval in figure, the oval being compressed, slight, and 
sometimes a little curved or distorted. These bodies bear nothing in their interior 
but a red fluid, and a nucleus which is elliptical in shape and very indistinct. An 
instance here and there occurs in which a few molecules are contained in these cells. 
Why the coi-puscles of the chylaqueous fluid of this worm and of Matuta clymenoida 
(Williams) (fig. 33) should, contrary to the universal Annelidan rule, contain a pig- 
mented fluid, it is at present difficult to explain. 
In a species of marine (fig. 32) Nais, common on this coast, which I have named 
N. maculosa, the corpuscles of the peritoneal fluid are spherical cells filled with 
granules, the latter being grouped in the centre, and separated from the involucrum 
by a layer of limpid fluid. 
Fig. 33 gives another illustration of the bodies found in the peritoneal fluid of the 
Annelida. They are those of a worm which I have called Clymene arenicoida* . 
Fig. 34 represents those of this fluid in SIgalion Boa. In the genus Polynoe the 
peritoneal fluid exists in large quantities. In all species it is richly corpusculated 
and milky. The blood-system in SIgalion is subordinate. The blood-proper is 
colourless and incorpuscular. The branchial appendages are constructed like hollow 
tubes, with express view to expose the peritoneal fluid, and not the blood-proper, to 
the aerating agency of the surrounding element. The corpuscles figured (fig. 34) 
resemble those of scaly epithelium. They are pregnant with molecules and oil-cells. 
Fig. 35 illustrates another variety of these bodies, from the peritoneal fluid of a new 
worm, which I have named Matuta clymenoida. These corpuscles are bright red, 
like those of the chylaqueous fluid of Glycera. They are very abundant, and give to 
the whole worm a blood-red colour. They assume the form of flattened scales, 
bearing two or three molecules and sometimes a nucleus, being, from the scantiness 
of their contents, transparently delicate and filled with a red fluid. 
The contents of the peritoneal cavity of Aphrodita aculeata (fig. 36) approach more 
nearly to those of the Echinoderms than of the Annelida, It must be remembered, 
with reference to this Annelid, that the water which is admitted underneath the dorsal 
felt is quite distinct from that contained in the cavity of the jieritoneum. The 
former is erroneously described by all naturalists as corresponding with that found 
in the visceral chamber in the Echinoderms. It is the latter and not the former 
fluid which is the true homologon of the chylaqueous fluid of the Echinoderm, 
* A full description of the specific characters of these new species will be found in my Report on the British 
Annelida, Transactions of the British Association, 1851. 
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