646 
DR. T. WILLIAMS ON THE BLOOD-PROPER AND 
Thus in a brief phrase is expressed a structural principle which governs the forma- 
tion of the blood-corpuscle in all Mollusks. 
The Bryozoa are to the Molluscan what the Pycnogonidae are to the crustacean series. 
In the Bryozoa and Pycnogonidae the vital fluids are constituted in the organism into 
a system, in strict accordance with the chylaqueous. How perfectly these two 
instances prove that nature, in cases of simple organisms, gathers together and circu- 
lates the nutritive fluids on the type and plan of this system, and not on that of the 
true-blood ! This fact indicates in the former, with respect to the latter, a relation ot 
inferiority. In both the instances enumerated, the fl.uids notwithstanding exhibit an 
advance upon the true chylaqueous fluid, in the fact that the corpuscles are more 
highly organized, while the fluid itself is more perfectly fibrinized, indications both 
of a higher degree of vitalization. 
In the Tunicata the apparatus of the circulation is developed obviously above the 
standard of the former. A heart and arterial trunks are detectable. The blood cur- 
rents, however, are not determinate in direction. As in the larva of insects, the 
portions of the fluid which accumulate in the peritoneal chambers oscillate to and 
fro under the muscular contortions of the body ; presently, however, and at unequal 
intervals, it obeys the impelling force of the heart, and advances in a definite orbit. 
In the Cynthidee or Salpidse the fluids may be readily obtained for examina- 
tion*. 
It is colourless, and discovers very distinctly the property of coagulating. The solid 
elements (figs. 64 and 65), relatively to the bulk of the fluid, are scanty. Similarly to 
what was observed in the Bryozoa, the cells exhibit several vai’ieties. It is a fact of 
considerable interest, that the floating cells of all inferiorly vitalized fluids should be 
characterized hy variety tuore or less numerous, in the form, size and structure of the 
corpuscular elements. The adult type of the corpuscle in the blood of the tunicated 
Mollusk is marked by no other feature of constancy than that of the orbicular figure. 
Sometimes this form is modified into the flat circular; frequently the cells are simply 
nucleated, again they are destitute of this part. All those which may be reckoned 
as mature, contain, in addition to a nucleus, granules, forming more or less of the 
bulk of the cell. The cell-capsule is more evident in this class than in the former. 
If submitted to the action of an endosraotic raediuin, such as water, it fibrillates 
more obviously than the corpuscles of an iminixed chylaqueous fluid. This cha- 
racter is a mark of superior organization. 
In the class of the Lamellibranchiate Mollusks, the readiest and surest method ot 
observing the blood-corpuscles consists either in viewing them in motion directly in 
the branchial vessels, or in isolating the heart, placing it under the microscope and 
* For this purpose, in these animals, the tunic and branchial chamber should be opened freely ; the fluid 
occupying the cells of the space intervening between these two parts will be found to be true-blood, the cor- 
puscles of which, if thus obtained, should be carefully compared with those in the same specimen seen moving 
in the branchial vessels. 
