FISSION IN NEMERTINES. 21 
so that I cannot state the true length; but at first sight this 
end does appear entire and rounded off (PI. 2, fig. 1). 
In transverse sections (fig. 10) probably the most noticeable 
feature is the thinness of the circular muscles; so thin is this 
layer that it cannot be distinguished in transverse section 
through the middle of the body until longitudinal sections 
are called in to help:! the basement membrane is also thin. 
The two nerve-cords lie between the basement membrane 
and the circular muscles, and this position at once shows that 
the worm belongs to the genus Carinella; but as to its 
specific identity I cannot be so sure. I hesitate to confer a 
new name on the worm, as it bears a certain likeness to 
C. linearis, Montagu, which is described by M‘Intosh; and 
one of his two woodcuts illustrating this species (p. 206) also 
shows constrictions of the hinder end, recalling at once the 
phenomenon presented by the present worm, although the 
“ segments ” are not so nearly equal in size. But this point 
would not be of any moment, for in the stained entire worm 
(Specimen I1) there is less equality in the size of these “ seg- 
ments” than in the one I first noted and drew when alive. 
There is, however, a statement in M‘Intosh’s description 
which renders an identification doubtful, for he states that 
C. linearis is “ flattened,” and this is certainly not the case 
with my worm at any rate—transverse sections do not exhibit 
any flattening. M‘Intosh states that “the inner muscle of the 
body-wall shows a marked tendency to separate in the dorsum.” 
If this means that the longitudinal coat is traversed by a 
band of tissue in middle line my specimen agrees with his. 
Nevertheless no great weight can be placed on this fact, for 
Birger has shown that this occurs in probably all species of 
Carinella. But from the general description, and from 
quotations from Montagu’s MS., it appears at any rate 
probable that the present worm is C. linearis, for it agrees 
in habitat, and in the fact that it ‘‘ secretes a tenacious slime 
from its body, which, collecting sand, readily forms a covering 
1 The thickness of the circular muscle-coat has been intentionally exag- 
gerated in the figure. 
