314 Vniversittj of California Publications in Zoology [Vol. 11 



becomes thickened in the contracted condition (pi. 14, fig. 3) from 

 the thin layer at the base of the tentacle to its broad, dense tip. 

 The surface epithelium on the tentacle consists of two kinds of 

 cells, long cylindrical cells extending to the basal membrane, and 

 shorter pointed cells which end in a threadlike process (pi. 14, 

 fig. 7) which may or may not extend to the basal membrane. 

 Slender spindle-shaped cells are interspersed between those of the 

 columnar epithelium. Nematocysts are found in irregular-shaped 

 or round cells that seem to be crowded between the other epith- 

 elial cells, or in places supplanting the latter altogether. The.se 

 nematocysts are of two kinds, a large, oval, thick-walled type, 

 with a long tube and a large barb at its base and a smaller, more 

 oblong type with a long tube arising from a bulb-like process 

 and a small barb at the base. These are found largely in bunches 

 over the surface of the tentacle and even the surface of the eye 

 (pi. 14, fig. 6, ncm.). Lying at an angle to the other cells or 

 parallel to the basement membrane are large bipolar cells, each 

 of which contains a very large, roimd nucleus (pi. 14. fig. 6, n. c). 

 These are probably nerve cells. Multipolar cells are also inter- 

 spersed throughout the base of the ectodermal layer. 



The endoderraal cells which line the ring canal are of a long 

 finger-like form, extending from the basment membrane out to 

 the lumen of the canal. Their nuclei are somewhat ellipsoidal 

 in form. These same columnar cells become gradually differ- 

 entiated in the tentacle to very long cells, with blunt ends facing 

 the tube, and finely drawn-out pointed ends turned towards the 

 outside of the tentacle. These are the type found just underneath 

 the eye (pi. 14, fig. 6). Wedged in between their basal ends 

 are similar cells, with both ends, however, drawn out to a point. 

 A cross-section of the tentacle through the eye is shown in plate 

 14, figure 7. 



The general arrangement of the parts of the eye is shown in 

 plate 14, figure 5. The epithelium of the tentacle becomes thick- 

 ened to form the sides of eye cup, whose bottom is lined with a 

 semicircular mass of browTi pigment. The lens (Is.) body fits 

 into the hollow of the cup. The rest of the eye-spot is formed of 

 epithelial cells with varying functions. The whole structure of 

 the eye seems to rest upon the basement membrane. 



