642 
DR. T. WILLIAMS ON THE BLOOD-PROPER AND 
absence of the cell-capsule is readily observed. In dimensions these bodies are 
proportionately small. Those of Talitrus locusta and Gammarus pulex are charac- 
teristic examples (fig. 57). 
In the Paguridw, or Hermit-crab family, the blood-corpuscles are prevalently 
ovoidal ; instances, however, of the elliptical and spherical figures are remarked 
among them. In every typical character they coincide with the articulate model, — 
the nucleus prominent, and generally placed eccentrically. The corpuscles are gra- 
nular and the involucrum apparently wanting. They fibrillate when rupturing in 
the most striking manner. Those of Pagurus Bernhardii (fig. 58) will serve to 
exemplify this class. The blood of the Brachyourous Decapods is distinguished for 
its comparatively large and prevailingly spherical corpuscles. In all the pellucid 
nucleus is a prominent object; it is always near some point of the circumference. 
The granules are so large as to be readily individualized by the eye. The involucrum 
is so attenuated, if existent at all, as not to be appreciable. As in the blood of all 
other crustaceans, three grades of development may in this instance be recognised ; — 
] St, the pellucid, nucleus-less globule ; 2nd, the nucleated cell, with a few surrounding 
molecules ; and 3rdiy, the mature cell, in this case approaching the sphere in figure. 
The fibrillation of the cells is here too invariably remarked. In consequence of the 
legible size of the objects, it is possible to prove, with reference to the blood-corpuscles 
of the Crab, that the fibrillation observed during the rupture of the cell, arises from 
the coagulation of the cohesive liquid by which the molecules (not the nucleus), con- 
stituting the great bulk of the corpuscle, are filled. It is probable, therefore, that 
each molecule is a miniature factory for fibrine. The nutritious fluid of the Macrourous 
Decapods is little different morphologically from those already described. The cor- 
puscles, however, are more generally elongated, so that the oat-shaped constitutes the 
average form ; in all other respects they conform intimately with those of other 
Crustacea. Those of the Lobster, Cray-fish, Prawn, and Shrimp (figs. 59, 60, 61), 
wdll serve to illustrate the characters of the solid elements of the blood in this order 
of Crustaceans. It will be observed that they present, severally, slight variations of 
size and form, which coincide with the differences of species. But through them 
all there runs a continuous evidence of an essential unity of type. 
Arachnida . — The naturalist is scarcely prepared for the announcement that the 
morphous elements of the blood of the Arachnid constitute the terminal link in the 
fluid-chain of the Articulata. In all the spiders of this country the corpuscles of the 
blood occur under the character of minutely granular bodies, varying between the 
spindle-shaped and orbicular in figure. Though absolutely small, they are, relatively 
to the size of the body of the animal, as large as those of the Crustacean. They differ 
from those of the latter in the position and invisibility of the nucleus. It is seated in 
the geometrical centre of the body, and therefore indetectable, because surrounded by 
molecules which are the exact counterpart of those formerly described in the blood- 
cells of the Crustacea. Like those of the latter cells, the molecules of the blood- 
