NEMERTEANS 243 



Both sexes of each form were examined. Ova are shed by separate ducts forming 

 when required through the dorsal muscles and epithelium. Spermatozoa are shed just 

 above the lateral nerves (Fig. 15B). Ripe eggs are present in August. 



The examination of sections showed that the original identification of these worms 

 with Emplectonema echinoderma, Marion, was inadmissable on account of the extent of 

 the rhynchocoel. It is evident that there is a close relationship with Zygonemertes 

 virescens (Verrill) Montgomery, but there are also differences— the larger size, the absence 

 of a terminal sense organ, the relatively larger base to the main stylet, the larger number 

 of eyes, the greater number of nerves in the proboscis— which justify the establishment 

 of a new species. 



Genus Tetrastemma, Ehrenberg 

 Tetrastemma candidum, O. F. Muller, 1774 (Plate XV, fig. 15). 

 T. incisum, Stimpson, 1856. 



Thirty-five specimens were captured in attached and washed-up kelp roots from the 

 rocks at the entrance of the Bay. The lengths were usually about 10 mm., breadth 

 0-5 mm., but sometimes they reached 16 mm., breadth 075 mm. 



Form and colour in life. The body is round in section, tapering posteriorly to the tail. 

 The head is slightly broader than the body. The mouth is not visible. On each side of 

 the head there is a nearly vertical groove and occasionally a second pair of grooves can 

 be seen immediately behind the head. 



The colour is pale buff or light brown. The edges of the body appear transparent, and 

 the gut is visible through the skin. There are four eyespots forming the corners of an 

 almost perfect square. The posterior pair is just behind the anterior grooves. 



Form and colour of preserved specimens. In spirit the ratio of length to breadth is 

 altered— an 11 mm. worm being 1-5 mm. broad, and a 9-5 mm. worm 1-2 mm. broad. 

 The colour is bleached, and the eyespots cannot be seen either before or after clearing in 

 clove or anilin oil. 



Internal structure. The oesophagus and rhynchodaeum coincide and the common 

 opening is immediately ventral to the tip of the head. The head glands are thin and 

 small. They just reach the brain. There are lateral and dorsal strands, the former joining 

 together near the tip of the head to form a ventral strand. They open at the extreme end 

 of the snout. 



In the region of the anterior caecum the epithelium is about two and a half times as 

 thick as the circular muscle layer and the basement membrane together, while the 

 circular muscle layer is a little thicker than the basement membrane. The longitudinal 

 muscle is thin. The eyes are visible in sections deeply sunk in the muscles of the head. 

 Branches from the anterior caecum extend as far forward as the brain. 

 The cephalic slits are deep grooves almost completely ventral near the tip of the head. 

 They pass back, upwards and outwards and become canals sinking into the longitudinal 



