610 William Patten 



On C. edule I bave couuted fifty-one eye-bearing tentacles, — so 

 large that oiie could distinguìsh the pigmented band with a band lens, 

 — about the orai or anterior opening, and sixty-two, around tbe anal 

 one. At tbe tips of tbe tentaele, on tbe lips of tbe cup-like bollow. are 

 tufts of stiif, sense bairs. Cilia, as far as I could see, were not otber- 

 wise present on tbe tentacles. 



In tbe connective tìssue of tbe sipbo, beneatb tbe bypodermis, are 

 many irregulär aggregations of large, round cells filled witb dark brown 

 pìgment. 



Tbe remaining portion of tbe mantle is pigmentless, witb tbe ex- 

 ception of a narrow band on tbe sbell side of tbe mantle. 



Most of tbe tentacles are single, but I bave observed several eases 

 in wbicb tbe apex was forked , eacb end hearing an eye. Tbe bypo- 

 dermis is tbrown into many irregulär, circular folds: tbere are also 

 two remarkable, longitudiual ones, extending tbe wbole lengtb of 

 the tentaele, one on eacb side (PI. 31, fig. 113 x). At the end of tbe 

 tentacles, beneatb the band of pigment, is an orgau containing ali tbe 

 Clements characteristic of an eye. It consists of a rougbly spherical 

 mass of large cells , — witb sbarply defined celi walls and nuclei , — 

 wben living, containing a faint red coloring matter. Tbe periphery of 

 tbe cells is filled with fine granular protoplasm, wbicb gives them the 

 peculiar appearance represented in tbe drawiug (fig. 112). Wben fresh, 

 they are transparent and refractive, so that one may see througb 

 them the silvery light reflected from the argentea. The former, in 

 combinatiou witb the red light from tbe large cells . causes a brilliant 

 iridescent play of colors similar to that produced by tbe red pigment 

 and argentea of Pecten. Tbe extremely simple retina, — wbicb is ob- 

 long in sbape, the short diameter being at right angles to tbe pigmented 

 covering — , consists of five or six rows of cells, tbe ends of wbicb are 

 directedinwards, andrestupon tbe mass of connective tissue fibres wbicb 

 serve at once as a capsule and tapetum. Tbe opposite extremities, near 

 wbicb are situated tbe large, ovai and sbarply stained nuclei, appear 

 to terminate in single nerve fibres, wbicb pass out of the capsule, on tbe 

 side opposite the pigmented band, and, bending at right angles, extend 

 along the axis of the tentaele as isolated fibres. At the angle of eacb 

 of these cells, nearly opposite the large nuclei, is a small and poorly 

 defined celi containing a minute, but deeply stained nucleus. It seemed, 

 at times, as if I could distinguish an extremely delicate membrane be- 

 tween tbe retina and the red cells , but I canuot say with certainty 

 wbether it was really tbere or not. 



