KING CRAB. 



339 



attachment of muscles. It should be noted, however, that an analogous 

 structure occurs in Apus and some other Crustaceans. 



The Nervous System. The supra-cesophageal brain gives off nerves 

 to the eyes. United to the brain are two ganglionated and transversely 

 connected commissures forming a long oval cesophageal ring, giving off 

 nerves to the limbs, and continued into a ganglionated abdominal cord. 

 Ensheathing ring, ventral cords, and some of the nerves are numerous 

 blood vessels. 



There are two "compound" eyes lying towards the sides of the 

 cephalothoracic shield, and in front of these two more median simple 

 eyes. The compound eyes are covered by a layer of chitin continuous 

 with that of the shield, and the various eye elements are so remarkably 



distinct from one another, that 

 the eye might be called a group 

 of simple eyes. 



The Food Canal. Worms and 

 the like seized by some of the 

 pincers, are partly masticated 

 by the bases of the five pos- 

 terior cephalothoracic legs. The 

 mouth leads into a suctorial 

 pharynx, with chitinous folds ; 

 thence the fore gut bends up- 

 wards and forwards into a crop. 

 Separated from this by a valve 

 is the mid gut which extends 

 along the cephalothorax and 

 abdomen, and in the former 

 bears two pairs of large yellow 

 hepato-pancreatic outgrowths. 

 The hind gut is short and ends 

 in front of the base of the spine. 

 Two large reddish glands lie 

 in the cephalothorax, and open 

 in young forms at the bases of 

 the fifth appendages. They also 

 open internally, and may be 

 compared with the coxal glands 

 of spider and scorpion, with the 

 shell gland of Entomostraca, and 

 with nephridia (?). 



The Vascttlar System. The 

 heart lies within a pericardium 

 and is partially divided into 

 eight chambers, with eight pairs 

 of valved ostia. Haemocyanin is 

 present as usual as the respira- 

 tory pigment of the blood, and there are oval corpuscles. From an 

 anterior aorta, like that of the scorpion, two vessels are given off which 

 bend backward, unite with lateral arteries from each chamber of the 

 heart, and form a collateral vessel on each side of the heart. These 



FIG. 107. Limulus or King Crab. 



ch., Chelicarae ; op., operculum ; 

 a., anus. 



