MUSEUM OF COMPARATIVE ZOOLOGY. 29 
7. Regeneration. 
Like other Endoprocta, Urnatella has the capacity of regenerating 
its lost calyces. Leidy (’84, p. 13) had already observed this process, 
and Potts and I have (as previously mentioned) seen the same thing. 
Figures 3 and 2 (Plate I.) show some of the phenomena of regenera- 
tion. The formation of a new terminal calyx seems to be preceded 
by the formation of the stalk part of the new terminal individual. 
This new formation takes place in one of the segments near the distal 
end of the parent stalk. The terminal dissepiment of the segment, 
cutting it off from the outside world, is completely closed in its cen- 
tre by a cuticular plug. This cuticular dissepiment (Fig. 2, di. sep. 
at the left) becomes torn off from the lateral cuticula of the segment 
along one edge, sometimes, as in the figure, remaining attached at 
the opposite edge. I have given on Plate I. (Fig. 3) a drawing of 
such a regenerating stalk before the polypide has budded from its 
wall. The outer body wall has evidently taken the initiative in the 
process, and mesenchymatous cells have migrated in. The drawing 
(Fig. 3) was made from the living animal, and the mesenchymatous 
cells could be seen changing form like an amoba. The ameeboid 
cells also contained highly refractive granules, which I regard as food 
material. These granules were seen moving about in the cells as the 
latter changed in form. 
One striking feature of the young segment was the presence of two 
flickering organs, which I now fully believe to be flame cells with their 
tufts of fused cilia, I have elsewhere ('91, p. 39) called attention 
to the part played by amooboid cells in Paludicella on the nutrition of 
the young buds. I believe that the amoeboid cells here have the same 
function. 
Leidy ('84, p. 13) has suggested that the segments of Urnatella might 
function as statoblasts to preserve the species during the winter. Of 
the correctness of this suggestion I have no doubt. The ease with 
which regeneration occurs from the old segments, and the fact that in 
stalks in which the calyces have been for a long time lost one sees the 
cirri of the flame cells still flickering, show that the tissue surrounded 
by the thick cuticula of the segments has a great capacity for retaining 
life, and, under favorable conditions, for reproducing lost parts. In their 
róle as statoblasts, the segments need the yolk stored up in their cells 
during the summer. 
