412 Prof. H. James-Clark on the Anatomy and 
the outline of the latter is hkewise as variable as that of any 
other similar form. 
§ 5. Tar Locomotive Orcans.—The locomotive organs are 
divided into three quite distinct sets, and appear to have as 
many diverse offices. They are all situated at the extreme 
posterior end of the body. Taken in their order, they stand 
thus :—lIst, a veil, or membranous annular margin (f, f!) ; 2nd, 
a row of vibratile cilia (7), which lies immediately behind the 
veil; and 3rd, a complex “adherent organ,’ in the form of a 
circle of centrifugal hooks (figs. 10, 17, 18, 4) and centripetal 
rays (2) which are firmly attached to the truncate posterior face 
of the body. 
The velum (f, f!) is merely an excessively thinned margin of 
the abruptly expanded, truncate, circular base. It has a breadth 
which is at least one-third as great as the length of the vibratile 
cilia (g), which are attached in a single row immediately behind 
its basal edge (fig. 17, f°). The free edge (f!) of the velum is 
smooth and regularly curved. It is not very difficult to dis- 
tinguish from the closely set row of cilia (g) just posterior to it. 
Although these cilia move so uniformly in concert, or in regular 
succession, as to appear at times like a vibrating frilled margin 
(fig. 10), yet when they are nearly quiet the veil may be dis- 
tinctly seen (especially with a one-eighth-of-an-inch objective) 
as an overlying, separately undulating membrane. With 
oblique light, at about twenty degrees from direct illumination, 
the velar edge is very conspicuous, and may be seen to be mar- 
gined by a thickening (fig. 17) which is easily traced across the 
whole width of the body, and at a decidedly different focus from 
that in which the bases of the vibratile cilia underlie it. Ina 
profile view it may be recognized as an abruptly terminating, 
marginal, tongue-like projection, vibrating by fits and starts 
(fig. 11, f), at the periphery of the circular base. 
The basal vibratile cilia (g) form a complete, symmetrical 
circle about the truncate posterior end of the body. They are 
more delicate and much longer than those of the anterior vibra- 
tory crown (d), and arise, m a single, closely set row, from a 
slightly projecting annular ridge which immediately subtends 
the line of attachment of the velum. This annular ridge, as will 
be seen presently, is the border (figs. 10, 17, 7!) of the ad- 
herent organ. Owing to their excessive fineness, the close 
proximity in which they are set, and the almost uniform succes- 
sion with which one cilium follows the other in the series of 
vibrations, this system gives to the unaccustomed eye the im- 
pression of an undulating frimge-like membrane, when it is 
viewed with only a moderate magnifying-power; but with an 
amplification of five hundred diameters, if the objective be a 
