20 BULLETIN OF THE 
alimentary tract, in the later stage the cocum has already begun to form, 
as in Phylactolemata, by an outpocketing of nearly the whole of the 
lower wall of the stomach. (Compare also Plate I. Figs. 7, 8, and 9.) 
Very soon after the establishment of the alimentary tract, and between 
the stages shown in Figures 24 and 25 in sagittal section, there begin 
to appear organs which have a very considerable phylogenetic signifi- 
cance; namely, the lophophoric ridges, ring canal, and tentacles. 
The lophophorie ridge is a fold which surrounds the mouth, and from 
which at intervals tentacles arise. The ridge, however, arises before the 
tentacles. The general position of the ridge, as well as its method of ori- 
gin, may be learned from an inspection of a series of sections of the age 
of those shown in Figures 31-34. In a section lying near the oral 
end of the bud (Fig. 33), one finds two spaces, — a lower, which is that 
of the stomach, and an upper, the oosophagus and atrium. This upper 
space is broader above than below, and the cell layer which lines it is 
thick below, but above, or nearer to the body wall of the budding 
individual, it is thinner. The transition from one condition to the 
other is quite abrupt, and is marked by a salient curve (loph.). Ina 
section near the anal end of the bud (Fig. 31), it will be seen that here 
too the inner layer is thick below and thin above. The characters men- 
tioned are still more strikingly shown in the median section, Figure 32. 
That the differences in thickness of different parts of the inner layer are 
recently acquired modifications of an earlier simpler condition is indi- 
cated by comparing Figure 32 with Figure 30, which is from a younger 
bud. The series of points (loph.) of transition from thick to thin epi- 
thelium forms on the reconstructed polypide a curved line, convex above, 
This line is the ridge of the young lophophore (compare Fig. 25, loph.). 
I have said that the lophophoric ridge arises before the tentacles, The 
evidence for this assertion is found in a series like that referred to above, 
where, although the ridge exists along the entire side of the atrium, 
one finds nascent tentacles in the middle region only (Figure 32, left 
hand). 
As Figure 25, of a later stage than Figures 31-33, shows, the lopho- 
phore curves downwards rapidly at the anal end, so that it here lies at 
right angles to the axis of the rectum, but does not extend at all beyond 
the anus. Orally, there is in the median plane only the slightest trace 
of the lophophoric ridge. By the formation of this ridge in the wall on 
each side of the atrial chamber, the original atrio-pharyngeal cavity has 
become separated into two regions. The space lying within or below the 
ridge forms the pharynx and the intertentacular space ; that lying with- 
