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 caeca, 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 amoeboid cells. These interspaces seem to represent 

 enlarged blood sinuses (a haemoccele), rather than a true body 

 cavity or ccelom. One of the spaces forms the blood-con - 

 earning 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 (via 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 antennae, 

 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 



