HABITS, ETC., OF CEREBRATULUS LACTEUS. 107 



of the sheath which lies above the oesophagus^ as can be seen 

 in jSg. 4. 



Its large anterior end is continuous with the walls of the 

 sheath just in front of the ganglionic commissure, while its 

 small posterior end is fastened at a single point where the 

 oesophagus joins the intestine. As the proboscis itself is 

 several times the length between these two points of attach- 

 ment it is coiled very closely. Furthermore, being attached 

 at the posterior end, it follows that it must always be of 

 double thickness, with a blunt anterior end when everted. 

 This increases its strength for prehension and burrowing, 

 and does not seem to detract from its delicacy as an organ 

 of touch. 



Food. — This species of Cerebratulus is almost wholly car- 

 nivorous, and feeds upon other worms which frequent the 

 mud between tides, showing a decided preference for Nereis. 



Several times both Nereis and Nemerteans were placed 

 in the same dish when obtained ; the former were found 

 to have been swallowed by the latter on reaching the labora- 

 tory half an hour later. The Nereis is always swallowed 

 tail first (fig. 1), which is exactly the opposite of the method 

 usually followed by carnivorous animals, but is occasionally 

 found in other carnivora, as when a snake swallows a frog 

 or toad (23). 



In such cases the animal swallowed is usually defenceless, 

 while its captor is well armed, but in the present instance 

 these conditions are exactly reversed. And it is very hard 

 to understand how a Nemertean, which has neither teeth nor 

 jaws, nor indeed offensive weapons of any kind, can yet over- 

 come a well-armed Annelid nearly as large as itself. The 

 head of the Nereis, with its powerful jaws, is left entirely 

 free, but although I have seen the victim wriggle frantically 

 in its efforts to escape, until it finally disappeared down its 

 captor's throat, it never made any attempt to bite. This is 

 the more remarkable in view of the well-known fact that when 

 two Nereis come together they almost invariably fall upon 

 each other tooth and claw, and often inflict very severe 



