634 
DR. T. WlLLlAiMS ON THE BLOOD-PROPER AND 
alone is submitted to the process of aeration. Therefore the agency of the floating 
corpuscles is not essential to the respiratory action of oxygen on the blood. This 
fact, which is unequivocal, is promissory of future discoveries. 
Relation between the Blood-'projyer and Peritoneal Fluid. — The physiologist cannot 
view with unconcern the question which relates to the mode in which the two fluids 
now described in the Annelida stand related to each other. It is scarcely required 
to observe, that what applies under this head to the Annelida will prove no less appli- 
cable to the Entozoa and Echinoderms, in which also these two varieties of nutrient 
fluids coexist in the same individual. 
In all Annelida a peculiar and express disposition of the blood-vessels is observable, 
by which an extensive contact is secured between the blood-proper and the fluid of 
the visceral cavity. This arrangement is so strikingly a provision for the attainment 
of a particular object that it cannot be misinterpreted. In the anatomy of the Nais 
this is perfectly and beautifully seen. From the sub-ganglionic trunk long coiled 
vessels proceed, describe several convolutions in the midst of the fluid, and in a 
jyerfectly naked and unsupported state, curve dorsally, still surrounded by the ehyl- 
aqueous fluid, and empty themselves into the great dorsal trunk. In Nais macu- 
losa (Williams) this distribution of the coiled vessels is still more readily demon- 
strated, in consequence of the bright red colour of the blood enabling the observer 
to trace the minutest vessels throughout their entire course. With respect to these 
vessels there is one remarkable fact to be stated, namely, that they maintain their 
singleness or individuality from their point of origin to their termination ; they do 
not branch. In this fact is seen a beautiful provision against injury during the 
contractions and elongations of the body. The slender column of blood contained 
in these vessels, is directly and throughout its whole course exposed to the agency of 
the peritoneal or chylaqueous fluid. The agency of this fluid is obviously of a two- 
fold character; it first replenishes the blood-proper with the chylous materials by 
which its healthy constitution is maintained, in other words, the coiled vessels absorb a 
chylous pabulum from the peritoneal fluid ; this process of chyle absorption may not 
be exclusively confined to these vessels ; those distributed over the parietes of the 
intestine may participate in this function ; and, secondly, the peritoneal fluid acting 
as a reservoir for the oxygen of the external element, forms to the coiled vessels a true 
aerating medium, the process of breathing being thus internal. In its application 
to the Entozoa this view of the mechanism of respiration acquires the highest interest. 
It is the true method of respiration in all Entozoa. The physiologist will now I trust 
definitively comprehend the breathing function in these parasites, though destitute of 
all semblance of external organs of respiration"*. 
One more question remains to be considered. What is the physiological meaning of 
this methodical contact between the two fluid elements of nutrition in the Annelida} 
That the blood-proper in degree of organization (vitality) is higher than the chyl- 
* In another communication I hope to enter at length into the demonstration of this subject. 
