8 BULLETIN OF THE 
in Figs. 13 and 14 being equally magnified), and their boundaries 
seem to be at some points discontinuous. Finally, in the basal seg- 
ment we find all trace of cell boundaries lost, and the central space 
filled by a mass of large and small yolk globules, nuclei, and proto- 
plasmic débris (Plate II. Fig. 8). 
The series of stages in the formation of yolk, which are shown in suc- 
cessive segments of the same stalk, points to the conclusion that yolk is 
in this case formed inside of the cell by a fusion of many excessively 
small granules, —a conclusion similar to that reached by Stuhlmann 
(87, p. 23) for the eggs of a Teleost. Hand in hand with the develop- 
ment of yolk there seems to go a diminution in the amount of proto- 
plasm, which therefore seems to be broken down in the process. The 
details of this process resemble remarkably those of the formation of 
the yolk in the statoblast of Phylactolsoma, for an accurate description of 
which we are especially indebted to Braem (90, p. 76). 
Urnatella is quite unique, so far as I know, among all Endoprocta in 
the storage of food material in its stalk. This is doubtless of high 
physiological importance, as I shall try to show later. 
Septa occur at the constrictions between segments, and separate the 
latter from one another. They are composed of a circular fold of ecto- 
derm, whose free edge surrounds a small opening, through which spindle- 
shaped vacuolated mesenchymatous cells pass. The adult condition is 
easily interpreted by reference to the development, an early stage in 
which is shown in Figure 24 (Plate IV.). Between the layers of the 
ectodermal fold a perforated disc of cuticula — continuous at its outer 
edge with the superficial cuticula — becomes laid down. This cutica- 
lar disc increases in thickness with increasing age. 
The most distal septum, which separates stalk and calyx, is more 
complicated than the others. The complication is due to the fact that 
mesenchymatous cells have placed themselves in and above the opening 
of the septum, and havo flattened themselves out perpendicularly to the 
axis of the stalk, while still allowing the vacuolated cells to pass at 
their margins into the calyx from the stalk. Thus the transversely 
flattened mesenchymatous cells appear to send out horizontal processes 
between the tubular cells (Plate IV. Fig. 25). 
The flattened cells which lie above the opening of the septum are 
seen, in longitudinal section of the stalk, to be arched over the opening. 
It results from this that the smaller, lower cells lie partly enclosed by 
the larger upper ones (Plate III. Fig. 18). 
A septum between stalk and calyx agreeing even in detail with that 
