MUSEUM OF COMPARATIVE ZOÖLOGY. 25 
the body wall. In Figure 36 the line passing through the same points 
makes an evident, but not very large, angle with the body wall. This 
line has undergone, then, a slight change of position only. The axir 
of the anal tentacles lies in both cases nearly parallel to the body wall, 
and so does the neural wall of the pharynx. The oral tentacles, on the 
contrary, whose axes in the earlier stage are directed perpendicularly 
to the body wall, lie in the later stage with their axes parallel to the 
wall; and the base of the lophophore, which in the earlier stage trended 
at its oral end parallel, at its anal perpendicular to the body wall, in 
the later lies throughout its whole extent in one plane perpendicular 
to the body wall. The axes of the oral tentacles have rotated through 
an angle of nearly 90° relatively to most of the other organs of the poly- 
pide. The canse of this rotation must evidently be sought in unequal 
growth in different parts of the polypide. A comparison of the length 
of the kamptoderm on the anal side in Figures 25 and 7 indicates 
that it has grown more in length than on the oral side. This excessive 
growth would tend to rotate the line vlv. er. — an. to a position perpen- 
dicular to the body wall. Since this rotation has not occurred to so 
great an extent ası,was to have been expected, we must look for a com- 
pensating growth on the oral side of the polypide, between wv. er. and 
the neck of the polypide, which shall be nearly equal to the excessive 
growth of the anal kamptoderm, and which must be outside of the oral 
kamptodem. These conditions of location are fulfilled only by the 
oral wall of the @sophagus, and it is by change of position and growth 
of this wall that the extension of the anal kamptoderm is nearly com- 
pensated for on the oral side of the polypide. By this growth in the 
wall of the csophagus the oral part of the ring canal has been brought 
to lie over the anal part, the sagittal diameter of the tentacular corona 
has been reduced, and the compressed lophophore has been transformed 
into a circular one. 
Concerning the number of tentacles, Dumortier et van Beneden (50, 
p. 46) observe that in the adult there are ordinarily 16, although 
individuals with 18 tentacles occur not infrequently, an observation 
which Kraepelin (’87, pp. 98, 99) confirms. In addition to these num- 
bers, I have found 15 and 17. The growth of the odd tentacle is quite 
interesting. The sections reproduced in Figures 60-62 (Plate VI.) will 
serve to illustrate a condition which I have quite frequently found in 
a polypide with 17 tentacles. In this particular series there are only 
15 tentacles. The successive sections abundantly demonstrate that 
the odd tentacle (*) is anal in position, and that it is younger than any 
