FISSION IN NEMERTINES. 19 
Fission in Nemertines. 
By 
W. Blaxland Benham, D.S¢.Lond., Hon. M.A.Oxon., 
Aldrichian Demonstrator in Comparative Anatomy in the University 
of Oxford. 
With Plates 2 and 3. 
Ir is a well-known fact that many Nemertines break up into 
pieces when irritated; but although this statement is current 
in text-books as well as in special memoirs the matter has 
received very little attention, and I find no account of any 
internal changes which may take place in the tissues of the 
body previous to the process of fragmentation. Indeed, it 
appears that the statement is made rather vaguely, and its 
application is scarcely so general as might be inferred. There 
is no doubt but that Carinella, Lineus, and other elongated 
and comparatively slender forms do fragment, and that these 
fragments can remain alive for a considerable time, as Dalyell, 
and later M‘Intosh have recorded ; and further, it appears that 
the anterior end of such a fragmented Lineus may produce a 
new posterior end, and M‘Intosh figures various stages in the 
formation of a head to amore posterior piece. As the specimen 
which he kept under observation lived in very unfavorable 
conditions of food, &c., he did not observe the completion of 
the head even after some months, but remarks that in a state 
of nature such a regeneration most probably takes place fre- 
quently.1. Further, we are left somewhat in doubt as to 
whether a Nemertine does of its own accord, and independently 
of irritation, normally break up into pieces. 
1 M‘Intosh, ‘Mar. Brit, Annelids: Nemertea,’ p. 125, 
