474 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



In individual larvae soon after the first formation of the axial organ strikingly 

 large vesicular nuclei appear which have quite the aspect of germ vesicles. They 

 surround themselves with an especially thick plasma zone, and their bulk appears 

 so considerable in contrast to that of neighboring cells that they give the impression 

 of young egg cells. 



Seeliger believes it is possible that this condition may indicate the animals 

 later to become females. 



The axial organ does not run in an absolutely straight line; clinging to the 

 curve of the stomach and esophagus, it is more or less sausage-shaped. The 

 posterior end lies on the border of the oral and aboral cojlome, while the anterior 

 proceeds into the column where it becomes extremely difficult to follow. 



At the end of the gut the axial organ bends toward the major axis and enters 

 the stem at the place on wliich in younger stages the ventral furrow in the foremost 

 end of the ccelome was present, between the first and fifth tubes of the chambered 

 organ. 



In the description of the origin of the chambered organ it has been mentioned 

 that mesenchyme cells accumulate on the evaginations of the ccelome in order to 

 take part in the formation of the cords running through the column, and the same 

 possibility is present here. 



On the other hand, it is conceivable that the walls of the chambered organ 

 on the sides toward the axis might through proliferation form a central string 

 which subsequently united itself with the axial organ of the calyx. 



Finally the axial organ of the calyx, which already in the early stages enters 

 the chambered organ as an isolated cord, may quite independently enlarge and 

 elongate posteriorly throughout the entire coliunn. 



In the oldest larvae of this stage the formation of trabeculas begins in the 

 aboral ccelome. In isolated instances single cells raise themselves up at right 

 angles to the plane of the epithelial wall, their broad bases dovetailed in among 

 the other cells, their outer ends projecting far into the body cavity. In these cells 

 the nucleus is usually displaced toward the middle. This process has taken place 

 much more extensively in the hydrocoele. 



HTDROCCELE. 



Like the vestibule, the hydrocoele ring, at first placed parallel to the major 

 axis of the body, gradually turns through an angle of 90° until it comes to rest 

 practically at right angles to this axis under the now transverse floor of the 

 vestibule. In this migration it maintains throughout the same relations with 

 the latter. 



The break in the continuity of the ring lies between radii I and V; that is 

 to say, in the same interradius as the pore. 



The hydrocoele is embedded in the thick basal wall of the vestibule. As it 

 passes from a longitudinal to a transverse position the more extensive becomes 

 the proliferation of cells from the vestibule floor, which will eventually form 

 the esophagus. 



