28 ARTHUE DENDT. 



Muscular Cells. — Certain spindle-shaped cells lying in the 

 membranous diaphragms of the exhalant apertures of the 

 flagellated chambers are probably muscular in function. The 

 cells in question are shown in fig. 24^ which renders further 

 description unnecessary. 



Nerve -eel Is. — The only cells which I have found in 

 Grantia labyrinthica to which a nervous function can 

 possibly be assigned are certain structures which occur around 

 the margins of the inhalant pores, as shown in fig. 31. 

 These cells are elongated radially in relation to the circular 

 pores which they surround. The nucleus is distinct and is 

 placed at the distal end of the cell, and the main mass of 

 protoplasm stretches from the nucleus to the edge of the pore, 

 where it ends in an expansion along the free margin. There 

 may also be indications of smaller processes given off near the 

 base of the cell. It is probable that the thickening of the 

 main protoplasmic process of each cell as it touches the margin 

 of the pore may simply indicate a retracted, sensitive, hair-like 

 process such as Stewart (21) and Lendenfeld (22) describe ; but 

 it seems also just possible that each nerve-cell naturally ends 

 in a sensitive plate or expansion at the free margin of the pore. 

 If we adopt the former of these two views the sensitive cells 

 will be seen to agree pretty closely in structure with those de- 

 scribed and figured by Stewart in Grantia compressa; but 

 I have met with no evidence of the grouping of the cells into 

 " synocils,'^ as described and figured by von Lendenfeld. Von 

 Lendenfeld, however, has also described single sensitive cells 

 C' Sinnes-Ganglienzelle^^) around the inhalant pores of his 

 Chalinissa communis, var. flabellum (23), which in struc- 

 ture and arrangement almost exactly agree with those found by 

 me in Grantia labyrinthica except that he figures the end of 

 the main protoplasmic process projecting for a short distance 

 beyond the margin of the pore. This slight difference may, as 

 will be gathered from what I have already said, be due to dif- 

 ferences in state of contraction in the two cases. It is interest- 

 ing to note that the sense-cells of Grantia labyrinthica 

 agree more closely with those of so different a sponge as 



