No. 3.] ORGANS IN PHASCOLOSOMA GOULDII. 385 



organs of the first type. The body of each of these bipolar 

 sense cells is of an elongated spindle shape, and it possesses 

 a large nucleus which is often differentiated by the stain 

 (PI, XXXIV, Figs. 6 and 7). The group of cells lies in the mid- 

 dle or just above the middle of the flask, and the long axes of 

 the cells are perpendicular to the ring muscles. The peripheral 

 processes of the cells are longer than those of the sensory cells 

 belonging to the first type of organ, as they must traverse both 

 the upper portion of the flask and the entire length of the bulb 

 before reaching the exterior. In passing through the neck of 

 the flask the peripheral processes of these sensory cells some- 

 times show spiral twists and turns very difficult to reproduce 

 (PI. XXXIV, Fig. 6). 



The fibers passing inward from the group of sensory cells 

 lie close together and occupy the central axis of the organ. 

 Emerging in a bundle from the base of the flask, they run for 

 a longer or shorter distance in a horizontal direction under the 

 epidermis and, crossing the circular muscle, enter one of the main 

 nerves coming from the central nervous system (PI. XXXIV, 

 Figs. 4 and 6). 



The peripheral process of each sensory cell passes up through 

 the neck of the bulb and at a little distance from the surface 

 becomes broadened and thickened in the manner described for 

 the sensory cells of the first type of organ. From this periph- 

 eral expansion a delicate process or hair extends through the 

 cuticula covering the bulb (PI. XXXIV, Figs. 6 and 11). In 

 some instances this sensory hair could not be traced quite through 

 the cuticula to the exterior, but such appearances were probably 

 due to defective staining, as in a large number of instances the 

 hair could be seen distinctly projecting beyond the surface. Im- 

 mediately over the center of the bulb in the region through which 

 the sensory hairs pass, the cuticula shows a marked concavity 

 of the outer surface, in some cases being so reduced in thickness 

 that only a line was visible (PI. XXXIV, Figs. 6 and 7). 



The organs of both types possess cells which are evidently 

 not sensory but supporting epidermal cells. No particular 

 attention has been paid to such cells and no description of 

 them appears necessary. 



