270 ZOOLOGY. 
The blood is driven by the heart through the arteries, and 
a large part of it, forced into the capillaries, is collected by 
the ventral venous sinus, and thence passing through the 
gills, where it is oxygenated, returns to the heart. 
The gills are appendages of the three pairs of maxilli- 
pedes and the five pairs of feet, and are contained in a 
chamber formed by the carapace ; the sea-water passing into 
the cavity between the body and the free edge of the cara- 
pace is afterwards scooped out through a large opening or 
passage on each side of the head, by a membranous append- 
age of the leg, called the “ gill-paddle” (Scaphognathite). 
The digestive system consists of a mouth, opening between 
the mandibles, an esophagus, a large, membranous stomach, 
with very large teeth for crushing the food within the large 
or cardiac portion, while the posterior or pyloric end forms 
a strainer through which the food presses into the long, 
straight intestine, which ends in the telson. The liver is 
very large, dark green, with two ducts emptying on each side 
into the junction of the stomach with the intestine. 
The nervous system consists of a brain situated directly 
under the base of the rostrum (supracesophageal ganglion), 
‘from which a pair of optic nerves go to the two eyes, and a 
pair to each pair of the antenna. The mouth-parts are 
supplied with nerves from the infracesophageal ganglion, 
which, with the rest of the nervous system, lies in a lower 
plane than the brain. There are behind these two ganglia 
eleven others; the cephalo-thoracic portion of the cord is 
protected above by a framework of solid processes, which 
forms, as it were, a ‘‘false-bottom” to the cephalo-thorax ; 
this has to be carefully removed before the nervous cord can 
be laid bare. A sympathetic nerve passes around each side 
of the cesophagus and distributes branches to the stomach. 
The nerves of special sense are the optic and auditory 
nerves. The eyes are compound, namely, composed of many 
simple eyes, each consisting of a cornea and crystalline 
cone, connected behind with ‘a long, slender connective rod, 
uniting the cone with a spindle-shaped body resting on or 
against an expansion of a fibre of the optic nerve, and is 
ensheathed by a retina or black pigment mass (Fig. 221 s) 
