NEMERTEANS 245 



The two blood vessels in the head form a loop. They lie one on each side of the 

 rhynchocoel in the brain region and subsequently dorsal to the lateral nerves, after con- 

 necting up with the dorsal vessel in the ventral wall of the rhynchocoel. Just before the 

 excretory ducts pass to the exterior the lateral vessels shift round inside the lateral 

 nerves and continue down the body beneath them. The excretory system consists of the 

 usual convoluted tubules close above the lateral nerves. In front of the anterior caecum 

 a duct leads to the exterior on each side above the nerve (on one side of this worm there 

 were two ducts). 



The brain is large for the size of the head, but it is compact and well defined. There is 

 a large proportion of fibrous tissue in both ganglia. The dorsal ganglia are smaller than 

 the ventral and the dorsal commissure is thinner and in advance of the ventral. The 

 cerebral organs are small sacs opening near the proboscis pore on the ventral surface. 

 They just reach the brain. The relations of brain, cerebral organs, excretory and ali- 

 mentary systems are shown in Fig. 17. 



This worm is very similar to Nemertopsis bivittata, Chiaje, with the exception of the 

 four eyes, but its internal structure shows that its affinities are with Tetrastemma rather 

 than Nemertopsis. 



Genus Oerstedia, Quatrefages 



Oerstedia maculata, n.sp. (Plate XV, fig. 11; Fig. 18). 



Five specimens (N 40) were collected from kelp roots from the outer beaches in 

 September. The lengths were 6, 7 and 8 mm. with breadths of 0-25-0-4 mm. The 

 largest specimen was 12 mm., breadth 0-4 mm. This species exhibited a semi-rigid 

 form like that of O. dorsalis, Abildg., and when in movement the head was often held 

 upon one side. In one of the worms this feature seemed permanent. A double eyespot 

 was observed in one specimen and ripe eggs were present in one. 



Form and colour in life. The body is round in section and short, with little distinction 

 between head and tail. The snout is blunt. Four large eyespots are apparent, but, as 

 shown later, the eyespots are double. They are placed in pairs one behind the other at 

 a greater distance than in Tetrastemma candidum. The colour is pale buff with one or two 

 indefinite and irregular small brown spots on the back. 



In spirit specimens the eyespots and markings are not visible, but the eyes on clearing 

 can be seen faintly as brownish marks. 



Internal structure. The epithelium in the stomach region is somewhat thicker than 

 basement membrane and the two muscle layers together. The basement membrane is 

 homogeneous and thicker than the circular muscles. The longitudinal muscle layer is 

 not divided into bundles. The oesophagus opens into the rhynchodaeum near the 

 opening of the latter to the exterior. A large unbranched anterior caecum is present, 

 reaching almost as far forwards as the brain. The proboscis is long and the rhynchocoel 

 extends almost the whole length of the body. The head glands form a compact mass, 

 spreading posteriorly and just reaching back to the ganglia. They open above the pro- 

 boscis pore. 



