GIGANTOCYPRIS MULLERI 241 



muscle. Since the valves of the shell cannot open, this appears to be the main function 

 of the muscle in this genus. The limbs are connected to the adductor muscle by a 

 powerful apodemal system in the centre of the body and laterally through an articulated 

 sclerite system (Figs. 3, 4). 



The articulated sclerite system is based on the same plan as that of Doloria. It has 

 been described in more detail, and in addition the muscular system attached to it has 

 been worked out (Fig. 5). 



As in Doloria, the pericardial space consists of an anterior pericardium containing 

 the heart and a posterior extending into the trunk region. The latter consists of a posterior 

 lacunar space coextensive with the criss-cross of dorsal longitudinal and circular muscles 

 and an antero-lateral tubular space which is an afferent canal leading from the general 

 perivisceral cavity into the anterior pericardium (Figs, ya, yb, 9). 



The arrangement of muscles which control the opening of the afferent canal is 

 described together with their relationship to the skeletal system (Fig. yb) and to the 

 cardiac nervous control (Fig. 9). 



The heart possesses an aortic and a pair of hepatic valves which, as in Doloria, are 

 splits in a membrane bounded by muscular strands. The muscles controlling the hepatic 

 valves are branches of the lateral subpericardial muscle. The muscles controlling the 

 aortic valve continue ventrally into the pericardial dilator. Both these muscles depress 

 the pericardial floor so that when blood is being sucked into the pericardium the hepatic 

 and aortic valves remain closed. The pericardial dilator appears to have no nervous 

 supply and may represent an independent effector organ (Figs. 9, 10). 



The heart and aorta of Gigantocypris have enlarged out of all proportion to the other 

 organs with the exception of the nauplius eye. The heart is, relative to that of Doloria, 

 about fifty times as big. 



The aorta sends off a minute labral artery medially and laterally an antennulary and 

 antennal artery. Postero-laterally it bifurcates into two branches which extend along 

 the dorsal surface of the lateral parts of the nerve ring and end at muscular valves. The 

 latter are formed of oesophageal dilators which extend from the ventral ectoderm just 

 behind the mouth and extend through the apertures in the tritocerebral region of the 

 nerve ring (Figs. 11, 12). 



The central nervous system consists of an anterior nerve ring and a posterior chain 

 system. There is no evidence that the latter represents a primitive condition. The nerve 

 ring is enclosed in a substantial but loosely fitting connective tissue sheath. This leaves 

 a very marked space between the brain and its neurilemma (Fig. 13, Plate XL, fig. 1 and 



Plate XLI, fig. 2). 



A basal ganglion system is present as in Doloria, but the ganglia are very large and 



more diffuse (Plate XLI, fig. 5). 



All the nerves leaving the central nervous system have been traced to their nerve 

 endings. In addition to the groups of segmental nerves supplying the limbs, there are 

 the nerves to the nauplius eye which have three roots and to the frontal organ which 

 has two roots. The rudimentary paired eyes have small roots. There are four separate 



