MUSEUM OF COMI'AKATIVE 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 amoeba. The amoeboid 

 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 amoeboid 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 

 role as statoblasts, the segments need the yolk stored up in their cells 

 during the summer. 



