222 DISCOVERY REPORTS 



muscles run dorsally, to meet the nauplius eye muscles. All these muscles and the 

 endosternite have the same relationships as in Doloria. The latter is not, however, 

 a thick plate as in the more typical Cypridinid but is a very thin tendinous sheet whose 

 actual limits are very difficult to determine. 



At its lower end the aorta divides into several branches. Medially it leads into a very 

 narrow but definite vessel between the frontal apodeme ventrally and the lower (or 

 hinder) wall of the brain dorsally (Fig. 12). I found no trace of such a vessel in Doloria, 

 but if it existed it would have been excessively minute. Its presence in Gigantocypris 

 is easy to establish because the lowermost wall of the aorta has spread over it a plexus 

 of nerve fibres (see p. 231), and these can be traced from the aortic tendon as a sheet 

 right through the nerve ring and then upwards to the frontal apodeme. The latter is 

 an extremely thin membranous plate in the median plane, so that blood passing from 

 the aorta through this channel would pass on either side of it into the upper end of 

 the labrum. I am therefore labelling this lacunar vessel the labral artery (Fig. 12). 



Laterally the aorta divides at its lower end into the two large vessels lying directly 

 on the nerve ring. In Doloria these two encircled the oesophagus and joined posteriorly 

 to form the supraneural ring vessel. In Gigantocypris they lie on the nerve ring but 

 do not join, and hence I call them the supraneural vessels. 



At their commencement they each give off a large vessel which runs forward and into 

 the antennules (Fig. 11). It can be traced in sections through most of the length of this 

 limb. Soon afterwards, and more laterally, they give off a very large vessel which runs 

 direct into the antennae where it opens in the neighbourhood of the antennal gland. 



Posteriorly the supraneural vessels narrow down to an extremely small opening 

 controlled, as in Doloria, by a valve (Figs, n, 12). This valve muscle is apparently 

 a modified oesophageal dilator, for its lower attachment is in series with the posterior 

 oesophageal dilators which are running in to attach to the endosternite. It can be 

 traced upwards, through the paired apertures of the tritocerebral region of the brain 

 to the supraneural vessel. At its upper end the muscle swings outwards and appears 

 to terminate in connective tissue in this region (Fig. 11). 



