EXPERIMENTAL OBSERVATIONS ON PENNATULIDS. 463 
The Spongy Tissue. 
The spongy tissue varies considerably in consistency 
among the members of the Pennatulids examined. 
In all the specimens of Pteroeides it is extremely dense 
and tough; in Pennatula phosphorea it is slightly trans- 
parent and delicate in texture^ while specimens of Pennatula 
rubra, Authoptilum, and Virgularia represent an inter- 
mediate condition in these and other respects. In all cases 
the spongy tissue appears upon microscopic examination to be 
made up of a more or less homogeneous deeply staining 
matrix, traversed in all directions by numerous canals 
having epithelial linings. They communicate by means of 
numerous apertures — usually ari’anged in longitudinal rows 
(figs. 13, 14, np.), with the large dorsal and ventral canals of 
the stalk and rachis, and at the base with the'exterior by 
means of a definite number of pores which appear to be 
constant for any given species (figs. 1, 2, 3, 4). 
The “ spongy tissue ” is capable of becoming rigid and 
turgid by the absorption of li(piids by its canals. On occasion 
these may be filled to distension, or the reverse, by the com- 
bined peristaltic action of the transverse and the longitudinal 
muscles of the body- wall. 
The “ epithelium ” lining the small canals of the “ spongy 
tissue ” is somewhat different from that lining the large 
canals of the stalk and rachis in that its ceils are more cubical 
in shape. This tissue is apparently characterised by an 
absence of the deeply staining mucus, the vacuolated, and the 
food-ingesting cells which form the main portion of the 
epithelium of the large canals. 
Kolliker (1870, p. 10) regarded the small canals of the 
spongy tissue as “ nutritive canals.” We have experimental 
evidence of the possession of a nutritive function on the part 
of the “ epithelium ” lining the hu’ge canals, but it is extremely 
])robable that the small canals of the “ spongy tissue ” are 
developed primarily for distension purposes. 
