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 peduncle 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 IX. fig. 7 x. 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 'VVimper^vulst 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. 7- With the exception of the constriction between Wimper- 

 wulst and polypite the feeding polyps have already been well described by 

 Leuckart, Gegenbaur, and others. 



Closely connected with the growth of the polyjiite is the development of 

 the tentacular knobs from the collar or Wimpenvnilst 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 diff'erent from 

 that which has been called the " embryonic knob," Figs. 9, 9*. The enlarge- 

 ment at the distal extremity increases in diameter (Fig. 22°), diff'erentiating three 

 lobes from the extremity of the growing knob. The two lateral of these lobes 

 by subsequent extension form those filament-like structures Avliich 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 shov,Ti 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, difier- 

 entiatetl from the coiled sacculus, which connect the distal and proximal ends 

 of the body of the knob, within the involucrum. These muscles have for a 



