108 
071 HoUenia, a Genus 
[Monthly Microscopical 
Journal, Aug. 1, 1869. 
This arrangement of the spicules gives the outer surface of the 
sponge a distinctly stellate appearance, the centres of the stems 
being the point of radiation of the secondary branches of the 
spicules. These quinque-radiate spicules measure about 1" * 5 from 
point to point of the cross-like secondary branches, and the length 
of the azygous arm is from 7"' • 5 to 1". 
Smaller stars, formed by the radiation of smaller spicules of the 
same class, occupy the spaces between the rays of the larger stars. 
The rays of each star bend irregularly, and meet the rays of 
the spicules forming the neighbouring stars. The rays of the dif- 
ferent spicules thus run along for some distance parallel to one 
another, and are held together by a layer of elastic sarcode, which 
invests all the spicules and all their branches. Between the rays 
of the spicules, over the whole surface, the sarcode forms an 
ultimate and very delicate network, its meshes defining and sur- 
rounding minute inhallant pores. 
At the top of the sponge there is a larger osculum, about 
3" in diameter, which terminates a cylindrical cavity which passes 
down vertically into the substance of the sponge to a depth 
of 5" 5"'. The walls of this oscular cavity are formed upon the 
same plan as the external wall of the sponge, and the stars, which 
are even more conspicuous than those of the outer wall, are due to 
the same arrangement of spicules of the same form. The ultimate 
sarcode network is absent between the rays of the stars of the 
oscular surface. 
The sponge-substance, which is about 2" in thickness be- 
tween the oscular and outer walls, is formed of a loose vacuolated 
arrangement of bands and rods of greyish consistent sarcode, con- 
taming minute disseminated granules, and groups of granules of 
horny matter, and endoplasts. 
Towards the outer wall of the sponge the sarcode trabeculse are 
arranged symmetrically, and at length they resolve themselves into 
distinct columns, which abut against and support the centres of 
the stars, leaving wide open anastomosing channels between them. 
The sarcode of the outer wall, and that of the wall of the oscular 
cavity, is loaded with minute spicules of two principal forms, 
quinque-radiate spicules with one ray prolonged and feathered, 
and minute amphidisci. 
Over the lower third of the body of the sponge, fascicles of 
enormously long delicate siliceous spicules pass out from the sarcode 
columns of the sponge-body in which they originate, through the 
outer wall, to be diffused to a distance of not less than half-a-metre 
in the mud in which the sponge lives buried ; and round the osculum 
and over the upper third of the sponge, sheaves of shorter, more 
rigid spicules project, forming a kind of fringe. 
I refer all the sponges which were found inhabiting the chalk- 
i 
