aoe EDITH M. PRATT. 
pauciflorum), while in others they are less numerous, are 
somewhat spindle shaped, and have only two or three pro- 
cesses (fig. 17, Sclerophytum densum). The fibril-like 
processes usually have a hyaline structure, are sometimes 
very long; and frequently fuse with each other, so as to form 
a more or less complete network (figs. 18 and 21), which is 
known as the mesoglceal nerve plexus. Where fusion has 
taken place the processes have a granular protoplasmic 
appearance similar to the cell contents. 
Many of the cells are intimately connected with the endo- 
derm cells of the zooids and canals! (figs. 17 and 18), but 
the connection between the cells and the ectoderm is less 
intimate (fig. 16). Occasionally a cell may be connected by 
means of its processes, with an ectoderm cell on one side, and 
an endoderm cell on the other. 
These cells, with their long fibril-like connections with 
ectoderm and endoderm, present, in the preserved condition, 
a remarkable likeness to nerve cells and fibrils occurring in 
other groups, but, beyond this resemblance, we have no 
evidence of their nervous character; moreover, the very 
intimate connection existing between the plexus and the 
endoderm (fig. 18), and its less intimate connection with the 
peripheral ectodermal tissues (fig. 16), throws considerable 
doubt upon the theory of its having a special nervous 
function. . 
In order to ascertain, therefore, its true nature and func- 
tion, I examined the plexus in living specimens. A com- 
parison of preserved preparations with the living plexus of 
cells in Aleyonium digitatum yielded results which are 
as interesting as they were unexpected. 
Thin free-hand sections of Aleyonium were examined in 
the living condition with moderately high powers,? when the 
1 The connection between the nerve fibres and the endoderm and ectoderm 
cells has been noted for the Alcyonaria by Hickson in Alcyonium, and 
Ashworth in Xenia and for the Madreporaria by Stanley Gardiner in 
Flabellum. 
2 Zeiss, No. 6 eyepiece, 53; oil imm. 
