114 
POPULAR SCIENCE REVIEW. 
occasioned, like the gods of Homer rescued from perils on the 
plains of Troy by an overshadowing cloud. This “ ink ” is so 
capable of preservation, that some extinct fossil forms have had 
their portraits taken by means of the very pigment they had 
themselves secreted so many ages bygone, and which had been, 
of course, buried with them. Certain kinds of cuttle-fish which 
have the cuttle-bone (or sepiostaire) replaced by an elongated 
horny structure amazingly like a quill pen (fig. 5), have been . 
called on this account, and on account of their ink-bag, pen- 
and-ink fishes.” 
The circulating system of true blood is much more complete 
than in the lobster. The blood is brought back from all parts 
of the body to a large vein (the vena cava), which bifurcates 
its branches, going one to each of the two gills. As soon as 
each branch has arrived at the base of the gill to which it is 
destined, it dilates into a contractile sac called a branchial 
heart,” which pumps the blood up into the gill. The two 
gills are formed on essentially the same type of structure as 
are the gills of the lobster, being similarly formed for subject- 
ing the venous blood to the oxygenating action of the air me- 
chanically mixed up in the water. As in the lobster, also, they 
are destitute of vibratile cilia. The very substance, however, 
of the gills themselves is contractile, and the blood having 
traversed them is transmitted in its aerated state to the ven- 
tricle, or systemic heart. It reaches that ventricle by two 
contractile vessels, which may be considered as auricles, each 
auricle taking origin at the root of one of the gills, and passing 
thence to the systemic heart, which thus (as also in the lobster) 
distributes to the system oxygenated blood only. 
The kidneys are in the form of two bunches of grapes, 
situated one bunch on each of the branches of the vena cava. 
Each is placed in a chamber termed the atrial or water chamber. » 
This chamber is part of the true somatic or body cavity, and is 
separated from the perivisceral cavity {i.e. from that which 
surrounds the intestine, &c.) by the mesentery enclosing the 
viscera. 
The renal secretion (urine) is washed out, as it were, by the 
water of the atrial chamber, which chamber communicates with 
the pal Hal cavity by two small openings, one on each side of 
the anus. 
The nervous system is well developed, though very con- 
centrated, and consists mainly of what are primitively and 
essentially three pairs of ganglia, named respectively “ cerebral,” 
“ pedal,” and “ parieto-splanchesic.” The two latter, however, 
are quite fused together. 
The cerebral ganglia may be considered as representing the 
brain, and thence issue the nerves of sight and smell. This 
