CHYLAQUEOUS FLUID OF INVERTEBRATE ANIMALS. 
641 
the peripheiy of the system is lacunose. The history of the evolution of the fluids 
of these microscopic animals is yet to be known. The illustrations delineate faith- 
fully the blood-corpuscles of Daphnia, Cyclops, and Branchipus. Magnified 420 
diameters. 
The fluids of the lowest crustaceans present all the essential features of the chyl- 
aqueous system. The Picnogonidce afford the best examples. In these inferior 
genera^ the digestive caeca float in the general cavity of the body. The space which 
intervenes between them and the integumentary exterior is filled with a colourless 
corpusculated fluid. The oscillations of this fluid are irregular, excited and 
sustained by the constant action of the arms and the undulations of the alimentary 
caeca. The corpuscles of this fluid are, relatively to its volume and to the size of 
the animal, very large. They depart as much from the normal articulate type as 
those of the embryonic fluid of the Insect do from those of the blood of the perfect 
animal. The inferior structural character of these bodies becomes expressive of a 
corresponding simplicity in the composition of the fluid. The walls of the cavity 
lodging the nutritive fluid in the Pycnodon are not ciliated. The corpuscles are 
spherical bodies, having an obvious cell-capsule, molecules, but no nucleus. This, 
like all other true chylaqueous fluids, is aerated at every part of its course throughout 
the body. Hence the absence of that which the simple nature of the fluid does not 
require, a special apparatus for respiration. 
Nothing is yet known of the morphological characters of the nutritive fluids in the 
embryo condition of the higher Crustacea. The fluids also of the adult animals, 
though easy of investigation, remain almost wholly undescribed. Mr. Wharton 
Jones, in his memoir in the Philosophical Transactions*, alludes only to the instances 
of the Lobster and the Crab ; on comparison, however, it will be seen that between 
his delineations and mine there are wide differences. 
In Caprella linearis {Lcemodipodes, Cuv.), it is an easy process to observe the blood- 
cells circulating in the branchial appendages depending from the inferior surface of 
the body. They occur under three discernible varieties: — 1st, simple, non-granular, 
non-nucleated, pellucid, spherical globules (fig. 56) ; 2nd, more or less orbicular 
bodies, of which the bright nucleus is prominent visible, and a mass of slightly 
refractive molecules ; 3rd, the fact, characteristic of all blood-cells falling under the 
denomination of the articulate type, of the apparent suppression of the cell-capsule. 
In this species the blood-corpuscles are large relatively to the proportions of the 
body. On bursting in the field their contents Jibrillate in a very obvious manner. 
In every observation I have been attentive to note this interesting fact ; it may avail 
some future theorist. 
The blood of the Amphipodce is distinguished for the prevailing orbicular character 
of its floating cells. The elliptical figure seldom occurs. The nucleus is more cen- 
trally situated, and therefore less visible than is common among the Crustacea. The 
* Op, cit. 
