112 



OHAS. B. WILSON. 



formed again^ but several removals produce a marked dimi- 

 nution in the amount secreted. This abundance of mucus 

 gives some of the smaller forms the ability to crawl back 

 downward on the surface of the water, after the manner 

 of nudibranchs, the mucus forming a sort of float, and being 

 firm enough to give the animal a purchase for its muscles. 

 Mcintosh states (34) that "if a Nemertean is raised from 

 the surface on which it crawls it always clings most perti- 

 naceously by the anterior end ; indeed it would appear that 

 the lips exercise a kind of sucker-like action, or at least that 

 the flattened under-surface of the snout does so." 



I have never been able to verify this observation on Cere- 

 bratulus, for I could not see that one portion clung to the 

 supporting surface any more than another. But the head 

 and anterior oesophagus are usually kept in contact with the 

 surface, while the other portions of the body are often 

 removed temporarily. 



Dismemberment. — Almost every scientist who has dealt 

 with the Nemerteans has noted their disagreeable habit of 

 dismembering themselves when irritated. But even the 

 specialists have not gone beyond a mere statement of the 

 fact except in one or two instances, while the best and 

 most recent monograph on the Nemerteans, that published 

 by Burger as the 22nd volume of the ' Fauna and Flora 

 of the Gulf of Naples,' does not even mention the habit 

 at all. 



We are informed that we must secure our specimens very 

 quickly, and kill them in something that produces instan- 

 taneous death if we expect to obtain anything more than a 

 handful of fragments for our pains ; but we are left to answer 

 for ourselves the many interesting questions that are sure to 

 arise. Do the Nemerteans ever fragment without irritation ? 

 If so, under what conditions and what advantage is it to the 

 worm ? 



After fission can both anterior and posterior fragments re- 

 generate, the one a new body and the other a new head ? 

 In answer to the first question, I had noticed for three 



