CHYLAQUEOUS FLUID OF INVERTEBRATE ANIMALS. 
627 
shaped bodies, which are not to be found in that of the adult. In this worm the 
chylaqueous fluid is not submitted to the process of aeration. 
In (Enone maculata the chylaqueous fluid, which at the reproduetive season is 
large in quantity, is charged thickly with corpuscles (fig. 24) of one uniform size 
and figure, and too minute to fall within the defining power of the microscope. 
They are mere amorphous molecules. In these worms the chylaqueous fluid is 
notconeerned in respiration. The branchise bear only proper blood-vessels. 
In the case of the Borlasiadse, Planariadse and Liniadee, the chylaqueous fluid is 
contained in the digestive caeea and diverticula. In some of the Planariadse, however, 
I have proved that a space does actually exist between the digestive diverticula and 
the solid structure of the body, which is lined hy a vihratile epithelium, and into which 
probably the external water is in some way admitted. By this water, thus situated, 
the contents of the digestive ceeca are aerated. The fluid oscillating in these csecal 
appendages of the stomach is thickly charged with corpuscles, which from their 
regular character prove this fluid to have already reaehed a high standard of organ- 
ization. They occur as elliptical cells in the Borlasia from which the illustration 
(fig. 25) was taken ; the fluid abounded also in small orbicular points, constituting 
the ‘ molecular basis’ of the digestive product. In this worm it is this fluid, and not 
the true-blood, that is aerated ; the latter system is too little developed. 
The genus Phyllodoce is characterized by the existence of a peritoneal fluid, liighly 
organized and corpusculated, and contained in a space which is almost undividedly 
continuous from one end of the body to the other ; the intestine being tied to the 
integument by means of bands, which leave the fluid free room to play from one 
segmental compartment to the other. In P . lameUigera the peritoneal fluid is colour- 
less, and contains flattened circular corpuscles, bearing a centric nucleus and filled 
with oily molecules (fig. 26). Cells of a pellucid character, and much more diminutive 
than the former, make up the mass of the morphotic elements. In the genus Phyl- 
lodoce the branehial organs are not at all penetrated by blood-vessels. The ehyl- 
aqueous fluid, by which their areolae are distended, must therefore be the direct 
recipient of the external oxygen. 
The Nereid worms are all distinguished by the existence of a large amount of cliyl- 
aqueous fluid in the visceral cavity. The septa of the segments are not complete 
partitions; the fluid therefore fluetuates with freedom from one end of the body to 
the other, and assists in a very material degree the locomotion of the worm. In this 
genus the fluid is characterized by the presence of corpuscles of large comparative 
size, and of generally an irregular figure (fig. 2/). In the season of autumn, as in 
some other Annelids, these corpuscles, which are the proper solid elements of the 
fluid, are superseded by true ova, one of which is represented in the centre of the 
figure. The peritoneal cavity in these familiar worms is always filled with a milky 
fluid, the organic quality of which cannot for a moment be doubted. The blood- 
proper is red, but fluid, that is, non-corpusculated, and the blood-system of vessels 
MDCCCLII. 4 M 
