54 BULLETIN! MUSEUM OF COMPARATIVE ZOOLOGY. 
parallel and perpendicular to the longitudinal axis, though less regular 
than the oblique ones, are easily recognizable. Owing to the surface of 
the bell being curved, the arrangement in quincunx is not as evident as 
I have represented it diagrammatically in Figure 20, but has more the 
appearance shown in Figure 19, where the oblique and transverse rows 
are somewhat curved, and the longitudinal ones diverge slightly as they 
pass backwards. 
The outer layer (Fig. 7, st/””) is composed of a series of ridges, or, 
more properly speaking, plates. These plates, cut crosswise, are shown 
in Figure 16 (st.”’), which represents a transverse section through the 
middle of the bell-shaped ciliated portion of the body, about in the place 
indicated by the line 16-16 in Figure 15. The plates are seen more 
clearly in the diagrammatic cross section shown in Figure 17, st”. 
In surface views of the animal each of the plates of the nipple appears 
to be split into two at the region of the fissure (Fig. 11, jis.) ; this, 
however, is only an optical illusion. Although the plates of the bell- 
shaped part are twice as numerous as those of the nipple-like part, 
there is no continuity between the two sets, the appearance of splitting 
being due to the overlapping of the anterior set over the posterior one. 
The nature of this overlapping (Fig. 12, fis.) may be seen in optical 
sections. The plates of the outer layer coincide with the 
longitudinal 
Their inner edges are slightly serrated 
longitudinal rows of cilia. 
(Fig. 8, esp.), owing to a slight inward prolongation of the plate wher- 
ever a cilium in passing through meets it. It is this condition which 
causes the interrupted appearance of the plates seen in tangential sec- 
tions (Fig. 20, esp.). 
The bell-shaped region is generally sharply marked off from the an- 
terior or nipple-like part by a deep constriction (Plate 1, Figs. 1-6); 
but sometimes there is a more gradual transition (Plate 2, Figs. Wy dP 
The boundary between the “bell” and the “ body” is ordinarily 
marked by a deep constriction (Plate 1, Figs. 1, 6), or a shoulder-like 
projection of the “body” beyond the outline of the “bell” (Plate 2, 
Figs. 7, 15). The place of this constriction may for convenience be 
called the lip of the bell, though the pendant central mass of the proto- 
plasm of the bell containing the nucleus often projects far behind this 
When the animal is at rest, the bell is of fairly regular and 
rim or lip. 
15), but the extreme mobility of the whole 
symmetrical form (Figs. 13, 
head region causes it when in action to take a great variety of shapes 
(Plate 1, Figs. 1-6). 
The protoplasm of the bell is differentiated into two distinct kinds, 
