NEMERTEANS 277 



these the basement membrane and circular muscles are equal in thickness and are to- 

 gether about one-quarter of the thickness of the epithelium. The oesophagus opens into 

 the stomach after the brain. There is no anterior caecum and the stomach is very long. 



The proboscis has fourteen nerves. One specimen had an accessory armature of two 

 reservoirs each with two stylets; another had two reservoirs each with four. 



The brain is small and the dorsal ganglia do not send fibres into the lateral nerves. 

 The cerebral organs are small and just reach the underside of the brain. The canals open 

 ventro-laterally. 



The specimen sectioned was an immature male. 



Tetrastemma validum, Burger, 1893 (Plate XVI, fig. 1 ; Figs. 52, 53). 



In colour and especially in form this species is the most easily recognized of the 

 southern Tetrastemma. Single specimens were taken from kelp roots in King Edward 

 Cove in 1927 (N 49) and 1929. In March 1930 thirty-eight specimens were caught by 

 the dredge with a mass of red algae. Other captures were at St. 175 (N 130) and St. 179 

 (eleven specimens — N 99). The lengths ranged from 8-5 and io-omm. to 35-0 and 

 40-0 mm. with corresponding breadths of o-8, 1-4, 2-5 and 2-3 mm. 



The body is stoutly built, flattened from above and fusiform. The head is pointed, 

 distinct from the body by a slight "neck". Cephalic grooves join under the head in a 

 wide V with its apex forward and from this junction another groove runs forward in the 

 mid-ventral line. There is a groove behind these at the shallow depression of the " neck ", 

 but this is incomplete dorsally. Sometimes the posterior part of the head is round and 

 broad, the anterior end being drawn out into a kind of beak. It has a distinctly shark- 

 like appearance, especially pronounced from the side. The colour on the back is dark 

 reddish brown, yellow-brown or purple-brown. The underside is white. On each side 

 of the head a very definite almost rectangular white tag shows up strongly against the 

 dark pigment. Just before this tag there is an encroachment of white on the pigment of 

 the head, and in this pigmentless patch lies the first pair of eyes. The second pair is 

 situated behind on the anterior edges of the white patches. 



Form and colour of preserved specimens. The body retains its shape to a great extent. 

 The anterior end is blunter than the tail. The back is convex, the belly flat or concave. 

 Very little colour remains in the specimens, but usually there is sufficient duskiness to 

 make the white patches faintly visible. 



Anatomy (Fig. 52). The head glands open near the tip of the head. There are at first 

 three strands towards the dorsal side but they soon completely fill the head. At the 

 anterior end of the brain the dorsal glands have coalesced, while ventrally there are still 

 small packets. The glands do not stain with haematoxylin. After the brain they persist 

 ventral to the branches of the anterior caecum. The epithelium is thicker than the sum 

 thickness of the other layers. 



The rhynchocoel extends to the end of the body and the nerves join just behind its 

 attachment over the gut. The proboscis possesses ten nerves (in one specimen twelve) 

 and has two accessory stylet reservoirs each with two stylets similar to the main stylet 



