MUSEUM OF COMPARATIVE ZOOLOGY. 27 
stolon-like body, which will become a basis of support for the new stock, 
the “basal plate.” One can thus account for the thickened cells of 
the under side of the stolon, which appear before detachment (Plate VI. 
Figs. 51, 57). The question remains, Do the median branches play a 
similar réle to the stolons? Ido not think they do, for the reasons, 
(1) that, having no basal plate, they are not physiologically fit for form- 
ing new stocks; (2) that I have found no new young stocks having 
one parent stem with one or two generations of budded individuals, — 
the condition of the median branches ; (3) that, on the contrary, one 
often finds such median branches persisting on even the lower segments 
of the stock. (Plate V. Figs. 35, 39, 40. Compare Leidy, ’84, pp. 8, 9, 
Plate I. Fig. 4.) Since the median branches frequently persist as a part 
of the parent stock, — they are not produced in the first place on every 
segment, —I conceive their function to be the increase of the number 
of proliferating points in the stock itself. 
Starting with the young stock, one can find all stages of growth up to 
the most complicated conditions (Plate V. Figs. 33, 36, 43, 44). Dur- 
ing the growth of the stock the basal plate gradually undergoes changes. 
The parenchyme becomes filled with yolk globules (Plate V. Fig. 49), 
and the cuticula becomes thick and dark. 
Concerning the morphological significance of the basal plate a few 
words must be said. I regard this asa stolon morphologically equiva- 
lent to the stolon of the Pedicellinide. In the latter group, as is well 
known, the individuals are budded from the upper side of a repent cy- 
lindrical stolon, which constantly produces new buds at the growing end, 
and which becomes separated into segments by the formation of trans- 
verse dissepiments. There is no such stolon in the adult Urnatella, 
which is sharply separated from the Pedicellinide by this single charac- 
ter. The presence of a stolon in the young stock indicates a derivation 
from an ancestral condition possessing a stolon in the adult. 
If, however, the “stolon” of the young Urnatella stock is homolo- 
gous with that of the Pedicellinid, we ought to find it, sometimes at 
least, giving rise to more individuals than two, and perhaps becoming 
segmented. Both of these conditions are occasionally fulfilled. Leidy 
observed that three, four, or even five stems may arise from a com- 
mon “ basal plate.” I have observed only three with certainty. Two 
cases of this are shown in Plate V. Figs. 48 and 49. In the first of 
the two cases distinct perforated dissepiments were observed dividing 
the stolon (basal plate) into three segments, out of each of which a 
single stalk arose. 
