10 DR J. STEPHENSON ON 
in area and not sharply defined (other authors). MaclInrosn’s: description seems to 
imply that he had had intermediate forms between the typical linearzs and rufifrons 
forms before him, and he states that he does not consider the red pigmentation to be of 
specific import. Both he and Jounin evidently consider it to be an intensification of 
the general colour of the head. 
The impression given by a consideration of all the above descriptions is, I think, 
that of a continuous series, somewhat as follows. In the first place, we have forms of a 
pale cream colour without any special pigment in the head; next, there may be a 
yellowish patch on the snout and a yellowish tinge in the cesophageal region ; then the 
tip of the snout may show special pigmentation—a deeper yellow, orange, or red—but 
the pigment is here not apparently granular in form. Again, while the general colour 
of the body is yellow or orange, the whole anterior part may be deeper in tint, the 
head being red, and the anterior tip most brilliantly coloured of all, but there is no 
sharp limitation of the red area; the pigment is partly diffuse, but also partly granular. 
As the next stage in concentration, the red pigment may be mainly visible as two red 
patches, with, it may be, again a particularly brilliant red spot in each. 
This condition may be reached without the appearance of any blue tinge. Asa rule, 
however, a blue tinge makes its appearance already in specimens with a pigmentation 
more diffused than that last described ; it may occur as a mere tinge in the red, or may 
give rise to the appearance of eye-spots by the aggregation of bluish-red pigment grains. 
Such spots may have a colour which, like that of the individual granules, may be 
described as bluish red, or a closer aggregation of the granules may result in a dusky 
purple or even a black. Of these ‘eye-spots’ there may be either two or three ; if two, 
they are symmetrical, one on each side; the third, when present, is median and anterior. 
The length of the Millport specimens, intermediate between the figures given by 
Bureer for his two forms linearis and rufifrons, also tends to obliterate the distinction 
between them. 
For the above reasons, I believe that the names rufifrons and bioculata ought to 
disappear as specific appellations, and that the peculiarities to which these names refer 
constitute merely colour varieties of C. linearis. 
On the Physiology of the Circulation in Cephalothria linearis. 
My observations on this subject are in the main confirmatory of those of MacInrosx 
on Cephalothriz (quoted below). In view of the little that is known concerning the 
physiology of the circulation in Nemertines, I may be permitted to call attention again 
to this form, in which the vascular phenomena appear to be particularly obvious. 
Under these circumstances it may perhaps be useful first to bring together, as far as has 
been possible to me, what has been written on the subject of the circulation of Nemertines. 
How contradictory, as well as scanty, are the statements concerning the physiology, as 
distinct from the anatomy, of this system, will appear from the following references. 
The most definite accounts are to be found in MacInrosx (10). With regard to the 
