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 debris (Plate 11. 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 Pliylactola^ma, 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 cuticu- 

 lar disc inci'eases 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 have 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 



