164 A. B. DAWSON 



c. Crescent-sha'ped bipolar cells 



Relatively few crescent-shaped bipolar cells were observed in 

 the earthworm, but they were distinctly shown by both the 

 methylene-blue and the silver-nitrate methods. All the cells 

 observed were remarkably uniform in size and form. Their dis- 

 tribution, too, was decidedly limited, as all the examples noted 

 were situated between the dorsal and ventral members of the 

 several pairs of setae. 



The cells lie in spaces in the outer portion of the circular muscle 

 layer quite close to the epidermis (fig. 5). The poles of the cells 

 (horns of the crescent) were directed outward and the processes 

 leaving both poles also passed outward, becoming lost eventually 

 in the basiepithelial network described by Dechant ('06) and 

 others. I have been unable to find any mention of a cell of this 

 type in the literature. Its significance will be discussed later. 



d. Long, slender, pyramidal, or spindle-shaped cells 



These cells are quite different from any already described and 

 were successfully demonstrated by means of the methylene-blue- 

 immersion method. The cells appeared only in preparations in 

 which the sense organs of the epidermis were selectively stained, 

 and in the use of methylene blue in this work it was generally 

 found that if the cells of the ventral chain and the intermuscular 

 tripolar and bipolar cells were brightly stained, the epidermal 

 sense cells were very faintly stained, and vice versa. Long, 

 slender pyramidal cells were never observed in silver-nitrate 

 preparations. In this connection it should be added that the 

 writer was unable, with the modification of Ramon y Cajal's 

 method, to secure satisfactory impregnations of the epidermal 

 sense organs. Kowalski ('09, figs. 47 to 50), however, following a 

 similar procedure, did not apparently encounter this difficulty. 



The staining characteristics noted above suggested at once 

 that these deeper-lying cells might be similar in nature to the 

 epidermal sensory cells, and both their position and the relation 

 of their fibers to other tissues strengthen this idea. All the ex- 

 amples (eight) of the slender cells were found on the ventral side 



