REPORT ON THE TETRACTINELLIDA. 
211 
a tliin layer of tissue, 0’02 mm. thick, crowded with microstrongyles and covered 
by the investing epithelium ; the outer layer of the cortex is thus barely repre- 
sented. Throughout the cortex, and particularly on the outer layer, are scattered 
oval pigment-cells, consisting of a thin cell-wall, enclosing numerous minute, 
spherical, transparent granules. The cells measure about 0'0158 by 0‘0197 mm. ; 
the granules about 0'002 mm. in diameter ; their colour in the tliin sections appears 
to be an ochreous-yellow. Eidley, in defining the characters of the genus Erylus, 
remarks that the sterrasters of the cortex are not united by ligaments like those I had 
described as binding together the sterrasters of other Geodine sponges ; but that they lie 
independently of each other. ^ After a careful examination of the structure of the cortex 
in this species I offer the following account of the relations of the sterrasters to the 
accompanpng tissue. The latter consists of a finely granular matrix which stains with 
haematoxylin, and contains fusiform cells dispersed through it. Near the innermost 
fibrous layer of the cortex, fine fibrillse, no doubt belonging to fibrillated cells like those 
which bind together the usual Geodine sterrasters, may sometimes be clearly perceived 
proceeding from the granulated surface of a sterraster, to which they are attached, and 
extending into the adjacent fibrous tissue. Again, by staining a fragment of the cortex 
with magenta or hsematoxylin and teasing out in glycerine, a film of fine fibrillse may 
frequently be observed attached at one end to a sterraster, and extending from it into the 
surrounding medium. That the granulations on the surface of these spicules should serve 
for purposes of attachment is what one would naturally expect from analogy with the 
function of the spines of the more usual form of sterraster, especially as like these they do 
not appear till the last stage in the development of the spicule, when it enters the cortex. 
On examining thin sections mounted in glycerine one will at first be unable to make 
out more than granular fusiform cells crossing the sterrasters transversely, but by close 
observation one may, in many cases, distinguish fine fibrillse extending from the surface 
of one of the spicules, and very rarely these can be traced into connection with an ad- 
joining spicule. So rarely, however, does this occur than it can scarcely be regarded as 
indicating the rule, and I therefore suspect that the fibrillated cells, instead of extending 
directly from the surface of one spicule to that of another, and for this indeed there is 
scarcely room, wrap round the surfaces of adjacent spicules and thus bind them together. 
So far then I can completely confirm Eidley’s statement as to the contrast between the 
structure observable in the cortex of a more typical Geodine sponge and of this ; but not 
as to the independence of the sterrasters ; they do not lie loosely aggregated like the 
orthodragmas in the cortex of Dragmastra, but are separately attached to fusiform cells, 
by which they are united together. 
The outer or microstrongylose layer of the cortex is continued down the sides of 
the chones, as the corresponding layer usually is in the Geodiidse, forming their walls, 
^ Ridley, Voyage of the “Alert,” p. 625. 
