CHYLAQUEOUS FLUID OF INVERTEBRATE ANIMALS. 
645 
In every Mollusk=^ yet examined the blood has been found to be colourless, not 
colourless like distilled water, but like very dilute milk. It is more coagulahle than 
any variety of chylaqueous fluid ; and from its viscidity it is undoubtedly more 
highly charged with the fibrinous principle than the latter. This fact results neces- 
sarily from the circumstance, that it constitutes in itself the entire fluid element of 
nutrition in the Mollusks, and that it is the seat of direct corpuscular agency. In 
this series the blood is invariably corpusculated. The proportion of the floating cells 
to the fluid varies however in different orders. In the Bryozoa and Tunicata, these 
bodies are relatively scanty. In the Cephalopods they are very numerous. Hereafter, 
in the progress of physiology, the law will be established, which recognises a vital 
pr'oportion between the measure of corpusculation, presented by the fluids and the 
‘ place’ of an animal in the series. One unaided observer cannot adventure upon a 
generalization which should have for its basis a multitude of “facts.” It is a remark- 
able law, which has now been demonstrated to preside over the blood of the articulate 
and the molluscan series, that in scarcely a single instance is it the seat of colour. 
In all cases except that of the Annelida the pigment is developed only in the cells of 
the solid structures. Among vertebrated animals, colour, and only the red colour, 
prevails without exception. Why should the blood-proper of the Annelids constitute 
an exception to a rule which applies to all other classes within the wide bounds of 
the invertebrate subkingdom ? These are queries pregnant with undelivered meaning. 
The Bryozoa, the lowest of the Mollusks, possess no vestige of a true-blood system. 
Neither a heart nor vessels under any shape can be discovered in any species. The 
nutritive fluid occupies the visceral cavity. It is imperfectly corpusculated, and 
oscillates in its containing chamber under the agency of muscular contractions. The 
branchiae are csecal tubes into which the fluid of the general cavity of the body freely 
enters, and in which it moves in fax and reflux currents. As foreshadowing a cha- 
racter of constant occurrence in the circulating system of Mollusks, this peculiarity 
should be specially noted. It is a specializing of the system in some part of its peri- 
phery while others remain degraded. It has been of late shown by the beautiful 
researches of Alder and Hancock, that in the Nudibranchiate Mollusks there are 
distinguishable three peripheral specializations, the portal, the branchial, and the renal* 
In these subsystems an approximation to a capillary reticulation of the conducting 
channels occurs. The branchial canals of the Bryozoa first typify the Molluscan law 
just defined. The morphous elements of the fluids in the Bryozoa, as formerly ex- 
plained, admit of easy observation in Laguncula repens, in any of the Flustroe, Lepralias 
or Escharce, most readily, however, in Bowerbankia. This consists of globules of 
various forms and size ; some are only opake, milky spherules, without nucleus or 
granules ; others are nucleated ; and a third variety, comprising the adult form of the 
cell, discovers a nucleus, small and centrally placed, surrounded by granules, con- 
stituting an orbicular corpuscle. 
* I speak of course within the bounds of my own personal observations. 
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