MUSEUM OF comparativp: zoology. 7 



Concerning the space into which the free end of the ciiTus projects I 

 can only conclude, from comparison with other cases where a flame cell 

 occurs, that this must represent the lumen of an excretory tubule. I 

 have not, however, been able in any instance to trace an individual 

 tubule to any considerable distance, or until it opens into any other 

 organ. One thing seems fairly certain, there is no morphological differ- 

 ence between those elongated clear spaces into which the cirri project 

 and the elongated vacuolated cells to which reference has already been 

 made. I am therefore inclined to regard it as probable that they are 

 one and the same thing. The vacuolated cells are developed by the 

 breaking down of the plasma of the elongated cells of the young stalk. 

 Before the metamorphosis is completed, one finds cells filled with clear 

 contents, in which lie scattered granules (Plate II. Fig. 15, cL tb. left). 

 Finally, even these seem to disappear (Fig. 15, cl. tb. right). Since 

 the tubules agree in size with these elongated, later vacuolated cells, 

 I conclude that their lumina are intracellular. Since the so called 

 vacuolated cells — many of which at least are, according to my view, 

 tubules — pass uninterruptedly from one segment to the next through 

 the central opening of the septa, there may easily exist continuous 

 tubules running from the basal segments into the calyx. 



The only excretory tubules which have been heretofore mentioned as 

 occurring in Endoprocta are the pair which lie in the calyx and open 

 into the atrium between mouth and rectum. Farther on, I shall 

 have occasion to inquire into the probable significance of the facts here 

 recorded. 



In specimens of Urnatella gathered in the fall and examined while 

 living, I found the basal segments filled with 3'olk granules (Plate I. 

 Fig. 4). Even in stocks collected in July, the basal segments contained 

 a greater or less amount of yolk. In passing from the distal towards 

 the proximal end of the stalk, one can trace the development of this 

 yolk, and since this is a matter of some general interest I have paid a 

 little attention to it. 



If we examine one of the middle segments of a stem whose basal 

 segment is full of large yolk spherules, we shall find reserve stuff form- 

 ing in some of the elongated cells. It appears as a fine granulation 

 throughout the whole cell, except immediately surrounding the nucleus 

 (Plate II. Fig. 13). Not all of the cells appear thus granular, for 

 others are at this stage vacuolated. Still later (Fig. 14) many of 

 the fine granules appear to have fused into larger ones, and these are 

 separated by clear spaces. The cells have enlarged very greatly (those 



