NEMERTEANS. 113 



metanenierteau structure, and contains twenty-two nerves. The length of the proboscis is 

 about half that of the body. 



The exerejtory tubules are first found in section just after the hinder end of the cerebral 

 orgfan. When first seen in section the tubules lie laterally and dorsally in the gelatinous 

 connective tissue just beneath the longitudinal muscle layer. As it issues from the nervous 

 ring the lateral blood vessel on either side makes a short bend to the lateral edge of the 

 body before taking up its position just dorsal to the nervous stem. The portion of the 

 vessel forming this bend is somewhat dilated, and the excretory tubules enter into close 

 relation with it. The excretory pore is situated about '5 mm. behind the termination of 

 the brain on either side. The duct in each case passes round the outer side of the 

 nervous stem and opens on the ventral surface directly beneath it. The excretory tubules 

 extend backwards nearly to the intestinal region, being all the way closely apposed to the 

 lateral blood vessel. 



Gonads undeveloped in all the specimens. 



The brain is large and round, and the dorsal ganglia have about 4 — 5 times the area of 

 the ventral in section. The dorsal commissure is very long and slender. The distance 

 between the nervous stems in the intestinal region is about half the width of the body. 

 A small median dorsal nerve occurs between the circular muscles and the basement mem- 

 brane. Just behind the dorsal commissure a small but well-defined nerve leaves the dorsal 

 ganglion on either side to run along the side of the proboscis sheath just above the 

 diverticula of that structure. It passes into the longitudinal muscles of this region. It is 

 not to be distinguished behind the oesophageal region. Whether this nerve supplies the mu.scle 

 fibres or whether it passes through the muscles and basement membrane to pass to the skin 

 is doubtful. The fact that it comes off the dorsal ganglion probably indicates a sensory 

 nerve. The nervous stems posteriorly form a well-marked supra-anal commissure. One pair 

 of neurochord cells is present in the brain. 



The cerebral organ is large, being in cross section about § of the area of the dorsal 

 ganglion at its largest. It lies exactly lateral to the dorsal ganglion and terminates 

 posteriorly at the same level. It possesses a cap of gland cells over its hinder portion, 

 which extends rather further forwards dor.sally than ventrally. The opening of the cerebral 

 organ is situated rather in front of the organ and exactly on the lateral edge of the body. 

 There are well-marked little longitudinal head furrows ("Kopfgriibchen") extending some way 

 dorsally and ventrally. The cerebral organ is supplied by one large nerve which comes off 

 the hind end of the dorsal ganglion. 



Numerous large eyes are present arranged in four longitudinal rows (cf. PI. IV. fig. 7.) 

 There are well-marked head glands, but these are short, not extending more than one-third of 

 the distance from the tip of the snout to the brain. 



12. Drepanophorus cerinus. (Burger. 1890.) (PI. IV. figs. 10, 11.) 



Literature. Btii-ger, 0. Zeit. fur Wiss. Zool., 50 Bd. 1890. 



Locality. Suvadiva atoll, Maldive Is. From 38 fathoms. 



The account given by Btirger is exceedingly short. The small size and the peculiar 

 structure of the cerebral organ, however, render the species fairly easy to identify. I have 

 added below a somewhat fuller account than that given by this author. 



G. 15 



