A NEW BRANCHIATE OLIGOCHATE. 329 
XIX, fig. 5); this is of course due to the contraction. The 
movements of the branchie are effected by muscular fibres 
which run across the cavity of the branchia from side to side ; 
these fibres are elongated, fusiform, with a central nucleus. 
They are sometimes branched, forming star-shaped bodies with 
the nucleus in the centre. 
The structure of the branchie (see fig. 6) is very simple ; they 
are covered by a firm cuticle, beneath which lies the epidermis. 
Bourne detected fine vibratile cilia upon the branchiz of 
Chetobranchus. I failed to discover any cilia upon the 
branchie of Branchiura. The axis of the branchia is occu- 
pied by a cavity evidently belonging to the celom; imme- 
diately beneath the epidermis is a layer of muscles which 
appears to be continuous with the circular layer of the body- 
wall; beneath this is the peritoneum. In Chetobranchus 
there is a capillary loop running up the branchiz in the ccelom, 
which in that worm, as in Branchiura, is prolonged into the 
branchie. In Branchiura there is no such capillary loop 
lying freely within the cavity of the branchia, but immediately 
beneath the epidermis is a blood-vessel on each side which 
gives a yellowish or even red colour to the branchia when 
examined under the microscope. I shall speak further of the 
blood-supply of the branchie in considering the course of the 
blood-vessels. 
Although the branchiz have an axial cavity, traversed by 
the muscular fibres which cause the contractions of the branchiz 
and lined with peritoneum, this cavity is not actually in com- 
munication with the body-cavity ; in the living worm the cavity 
of the branchia can be easily seen to be shut off from the 
ceelom by a diaphragm which moves synchronously with the 
contractions of the dorsal vessel. It becomes alternately convex 
and concave outwards : when convex, i. e. when forced forwards 
by the liquid of the celom, it projects some way into the 
interior of the branchia, and is very conspicuous ; it appeared 
to me to completely block all ingress of solid matter into the 
lumen of the branchia. The ceelom of this worm contained no 
freely floating corpuscles that I could discover; I am not able 
