MUSEUM OF COMPARATIVE ZOOLOGY. 165 
out of a thickened middle layer, which lies between those which first formed 
the bud. On the distal portion of the walls of the spherical base of the polyp- 
ites in this condition of growth many large lasso-cells arranged irregularly, as 
shown in the figure, make their appearance. At the base of the polypite 
where it joins the pedunele by which the feeding polyp hangs on the axis of 
the Agalma, there is a ferule-like structure, which has been called the “ Wim- 
perwulst.” From this body in older stages the tentacular knobs, and after 
them the tentacles, later arise, Plate EX. fig. 7%. As in its growth the polypite 
becomes older, Fig. 6, it takes on a more flask-shaped form, and the thick- 
ened median layer becomes reduced. in size, while the lasso-cells in this region 
of the polypite increase in number. The Wimperwulst retains about the 
same size as in the former figure. In the next stage in the growth of the 
polypite, a part of which is figured in Fig. 8, the enlargement of the proxi- 
mal end of this structure is still more diminished in size, and in the adult 
feeding polyp the reduction has gone so far that the swelling has completely 
disappeared, leaving between the Wimperwulst and the body of the polyp- 
ite a kind of constriction richly covered with lasso-cells. This adult form is 
figured in Fig. T. With the exception of the constrietion between Wimper- 
wulst and polypite the feeding polyps have already been well deseribed by 
Leuckart, Gegenbaur, and others. 
Closely conneeted with the growth of the polypite is the development of 
the tentacular knobs from the collar or Wimperwulst at its base. These 
bodies begin as simple buds, which elongate into hollow club-shaped structures 
of regular outline, Plate IX. fig. 22. In a somewhat later stage (Fig. 22%) the 
distal end of the cavity of this organ slightly enlarges in diameter. Lasso-cells 
are present in the walls of the proximal part of the immature knob. These 
figures show that from the very first this “adult knob ?is wholly different from 
that which has been called the “ embryonic knob," Figs. 9, 9%. The enlarge- 
ment at the distal extremity increases in diameter (Fig. 22°), differentiating three 
lobes from the extremity of the growing knob. The two lateral of these lobes 
by subsequent extension form those filament-like structures which I have repre- 
sented in the adult knob, Figs. 20, 21, b. The medially placed lobe, which is 
the extremity of the knob placed in the angle between the two lateral pro- 
longations, becomes the terminal sac (a, Figs. 20, 21) in the adult knob. 
The remainder of the half-formed knob coils itself together, passing into the 
future sacculus, while in its walls form those characteristic lasso-cells which 
distinguish this organ in the adult. Pigment also darkens its walls, and from 
its proximal part a circular rim is pushed out, which grows down around the 
sacculus enclosing it, in a sac which is shown in the figure of the adult knob 
as covering the whole sacculus, with the exception of the distal appendages, 
Fig. 21, e. In Fig. 20, e, this structure, which is called the involucrum, is 
drawn. back to expose organs within, which otherwise could not be well shown, 
The last parts of the knob to be formed are two muscular threads, differ- 
entiated from the coiled sacculus, which connect the distal and proximal ends 
of the body of the knob, within the involuerum. These muscles have for a 
