12 DR J. STEPHENSON ON 
at each end of the worm,” which is practically Maclnrosu’s statement; but he adds 
that this is very unsatisfactory and uncertain. 
Punnett, in his Addenda and Corrigenda to this volume of LANKEsTER’s Treatise (13), 
says that “‘in spite of what has often been written to the contrary, it is exceedingly prob- 
able that in most cases, if not all, the blood vessels are destitute of muscle fibrils; and that 
the blood is kept in circulation by the waves of contraction passing over the body-wall.” 
Finally Cox (6), in describing Carinomella, states that “ shortly behind the nephridial 
region the lateral vessels acquire muscular walls and are strongly contracted at intervals.” 
He does not describe vascular contractions in any other forms ; and in the general section 
of his work, under ‘“ Histological Structure,” after describing the muscular coat of the 
chief vessels, says: “The transverse vessels and many of the lacunz are without 
muscular walls, and even where muscles occur, the circulation of the blood is dependent 
mainly on the movements of the body as a whole, and as a rule passes backward and for- 
ward irregularly in any of the vessels.” 
The circulation in the lateral vessels of C. linearis can be seen in specimens 
compressed under a coverslip. The phenomenon appears as a series of waves, passing 
along in the situation of the vessels, laterally to the alimentary canal. The walls of the 
vessels are not themselves visible, and the waves manifest themselves as the rapid 
passage of a lighter streak or patch along the body of the animal. 
The rhythm is irregular. The waves pass in all cases through the greater part of the 
length of the animal, it may be from the region of the nerve ganglia anteriorly to the 
extreme posterior end. The passage of the waves was always rapid. 
In direction the waves may be either postero-anterior or antero-posterior; and 
these usually alternate, with, it may be, a second’s interval between the arrival of the 
wave at the head, and the starting thence of a wave in a posterior direction. The waves 
on the two sides may be almost synchronous; but I have observed a wave on one side 
only, quite unaccompanied by any indication of a wave on the opposite side. 
The specimens were, as a rule, motionless during the observation of the phenomenon. 
With regard to Cephalothiix, then, it seems allowable to conclude :— 
(i.) That there is a definite circulation in the lateral vessels, occasioned by a series of 
contractile waves alternately postero-anterior and antero-posterior. 
(ii.) That this is not due to contractions of the body-wall, nor to movements of the 
body as a whole. 
(ii.) And that it would therefore seem necessary to assume the presence of muscular 
tissue in the walls of the vessels. 
Emplectonema gracile (Johnst.) (= Nemertes gracilis). 
Near low-water mark, under stones, Balloch. Not uncommon. 
Length up to seven inches; proportionally very thin; not markedly pointed at the 
posterior end. 
