342 University of California Publications in Zoology [Vol. 20 



sides. Being thicker through, in this direction, too much of the light 

 is shut out. It will be noted that the oral whorl converges from both 

 sides toward the "center," while the aboral whorl converges from 

 only the right side. For this reason, the meeting place on the right 

 side of the animal is formed of diverging fiber ends (pi. 32, fig. 4). 

 On the left the fibers of the oral whorl meet the converging apex of 

 the aboral whorl (pi. 32, fig. 2). Thus the entire ectoplasm is supplied 

 with a thick complex of diverging fibers. 



Actual connections of fibers to the basal granules are figured in 

 plate 33, figures 7-12, and plate 35, figures 21. 25. Kahinsky (1910) 

 confirms the presence of these fibers, but calls them ciliary rootlets. 

 They can be made out clearly only in thin sections (not over 

 2.5 microns). 



The facts that in whole mounts and thick sections the neuromotor 

 fibers can be traced to the immediate vicinity of the basal granules 

 and that in thin sections actual connections can be seen are submitted 

 as proof that the ciliary rootlets represent the connections of the 

 neuromotor fibers with the basal granules. 



The figures cited above also show fine fibers connected to the inner 

 ends of the trichocysts. These also are believed to be neuromotor 

 fibers innervating the defensive organelles of the body. 



Fibers of the Cytostome and Cytopharynx 



The oral groove (fig. A, or. gr.) extends from the anterior end of 

 the animal to the region of the posterior two-thirds of the body. As 

 previously described, the peripheral fibers, only, underlie the surface 

 of this groove. They exhibit no special modification in this region. 



The cytostome is an elongated oval aperture extending obliquely 

 caudad from the posterior margin of the oral groove (fig. A. cyt.). 

 Around its margin is a row of peristomal cilia. Two fibers connect 

 the basal granules of these cilia with the neuromotor center. They 

 run one in each margin and are continued posteriorly into the 

 cytopharynx. 



The cytopharynx begins at the anterior margin of the cytostome. 

 From this point to the posterior cytostomal margin it is a V-shaped 

 depression (pi. 33, fig. 8). Then it becomes a subcylindrical structure 

 except at the extreme posterior end, where there is an enlargement. 

 The enlargement is not perfectly spheroidal (pi. 33, fig. 11), but is 

 broadly indented on the oral side. The posterior extremity of the 



