32 W. G. RIDEWOOD. 
The number of plumes is not constant. The commonest number is fourteen, 
but there may be as many as sixteen and as few as twelve plumes. A study of 
the buds shows that, as in Cephalodiscus dodecalophus, the full complement of plumes 
does not develop simultaneously, but successively, and the occasional presence of a 
very small plume among thirteen or fourteen large ones in a full-grown individual 
suggests that the number may be subject to increase even after the adult stage has 
been reached. 
Stolon. 
The stolon is stout, short as compared with that of C. dodecalophus, roughly 
circular in section, and with a pigmented and transversely wrinkled surface. It 
does not taper, but is of fairly uniform diameter; its free or posterior end is 
hemispherical, and from the margin of this extremity the buds are developed. 
The angle at which the stolon stands out from the body differs in polypides 
found in tubes and those found free (see p. 26). 
The longitudinal muscles in the stolon are disposed in the form of a thick- 
walled tube surrounding a mass of compacted coelomic corpuscles and trabeculae. 
There is no median septum in the greater part of the length of the stolon, it 
extends hardly beyond the base of that organ. 
There is little variation in the shape of the stolon. In a full-grown individual 
with many buds it is always short, cylindrical and stout; but from the wrinkling 
of the superficial epithelium one may conclude that the organ has been fixed 
by the preservative fluid in a condition of extreme contraction. As is explained 
later in the remarks upon budding, a large bud may develop at that end of its stalk 
which is attached to the parent stolon a small bud of its own. On the separation 
of the bud from the parent form, its stalk becomes its stolon, and the bud already 
present at its end, and those developed later, have relations to this stolon similar 
to those which the buds of the parent form bore to the parent stolon. The 
interesting feature to be noted here is that the stalk of the large bud in question is 
not always found in a state of contraction ; in most cases it is two or three times 
as long as the stolon of the parent, and is slender in proportion. 
If one assumes that the parental stolon is in a fully contracted state, the 
explanation of the granular mass in the middle of it is not far to seek. The stolon 
is to be regarded as a hollow structure, with the coelomic cavity traversed by 
connective tissue strands with the characteristic prominent lateral nuclei, and by 
an excessive diminution in the length of the stolon these threads and nuclei 
become all crowded together and form a dense core, the coelomic cavity as a cavity 
disappears in the stolon itself, and only remains recognisable in the basal part. 
In a male individual with large testes a limb of one of them may extend into the 
basal part of this granular core of the stolon. 
The question why the stolon of full-grown individuals is invariably contracted 
