290 PHYLUM ARTHROPODA. 
the large and complex digestive gland. The mid-gut, here 
as always, is the digestive and absorptive region, but both 
processes are carried on to a large extent in the digestive 
gland, which communicates with the mid-gut by two wide 
ducts. It is roughly three-lobed at both sides, and consists 
of an aggregated mass of czeca, closely compacted together. 
The gland is more than a “liver,” more even than a 
“hepatopancreas.” It absorbs peptones and sugar; like 
the Vertebrate liver, it makes glycogen; its digestive 
juices are comparable to those of the pancreas and the 
stomach of higher animals. The hind-gut is long and 
straight. It is lined by a chitinous cuticle, as its origin 
suggests. There are a few minute glands on its walls. 
Body cavity.—The space between the gut and the body 
wall is for the most part filled up by the muscles and the 
organs, but there are interspaces left which contain a fluid 
with amceboid cells. These interspaces seem to represent 
enlarged blood sinuses (a heemoccele), rather than a true body 
cavity or coelom. One of the spaces forms the blood-con- 
taining pericardium, or chamber in which the heart lies. 
Vascular system.— Within this non-muscular pericardium, 
and moored to it by thin muscular strands, lies the six-sided 
heart, which receives pure blood from the gills (wa the 
pericardium) and drives it to the body. 
The arterial system is well developed. Anteriorly, the 
heart gives off a median (ophthalmic) artery to the eyes and 
antennules, a pair of (antennary) arteries to the antennz, 
and a pair to the digestive gland (hepatic). Posteriorly 
there issues a single vessel, which at once divides into a 
superior abdominal, running along the dorsal surface, and 
a sternal, which goes vertically through the body. This 
sternal passes between the connectives joining the fourth and 
fifth ventral ganglia, and then divides into an anterior and 
posterior abdominal branch. All these arteries are con- 
tinued into capillaries. 
From the tissues the venous blood is gathered up in 
channels, which are not sufficiently defined to be called veins. 
It is collected in a ventral venous sinus, and passes into the 
gills. Thence, purified by exposure on the water-washed 
surfaces, it returns by six vessels on each side to the peri- 
cardium. From this it enters the heart by six large and 
