84 Dr. 8. Lovén on a remarkable Sponge 
spicules, boiled in nitric acid, has been a little damaged, its 
inner parts are altered; if the point is broken, there appears 
in the canal, and between two or more layers of silica, besides 
some gas, a black substance—the carbonized soft matter. If 
the point is not damaged, but the side, this substance is spread 
between the outermost layer and the next, but the canal and 
the inner layers retain their transparency unaltered. In one 
spicule a part of the canal and the interval between the inner- 
most and the following layer is filled with the dark substance, 
which has been pressed out right through a third layer, by 
very fine pores, at right angles from the longitudinal axis. 
From this it seems to follow that the canal, normally closed 
at the ends, contains a soft organic matter alternating with 
the lamelle of silica in such a manner that one of these is the 
exterior, and that the layers are perforated with minute pores. 
The fluid contents of the needle accordingly may be in contact 
with the exterior, and an exchange of substance take place. 
That this is really the case is shown by the manner in which 
branches are first formed, when the hitherto firm and straight 
lamellee, as if yielding to a force from the interior, without 
fracture, bend outwards with undiminished thickness, and, 
bulging out, soon take up in the interior a branch from the 
central canal. The silica of the exterior layers has its source 
in the surrounding parenchyma. The spicule is by degrees 
covered with new layers of silica. If an anchorate spicule, 
which is of the same structure, with central canal and lamelle, 
is brought mto contact with a needle, it is soldered to it, co- 
vered with layers of silica, and finally partly immersed in the 
needle, thick and with blunted outlines, whilst in the interior 
the originally slender and elaborate form is well discerned 
through the glassy mass. 
The spicules of our sponge are of various lengths. I have 
found them from 2°93 millims. in length and 0-047 millim. in 
thickness to 0°79 millim. in length and 0-01 millim. in thick- 
ness, the mean length 2°12 millims.,—the relation of length to 
thickness being in one as 100: 1°95, in another as 100 : 0°93, 
the mean relation as 100 : 1°42. 
The stem is continued into the head above its middle, and 
there ends conically. From that part proceed the spicules 
which give to the head its structure, form, and consistency 
(figs. 31, 32). Between the erect spicules of the stem, bundles 
of needles are inserted (fig. 33), which radiate in different 
directions (if with any regularity I cannot say), downwards, 
upwards, and to the sides. These bundles are light and firm 
as the stem, arcuated, gradually broader and somewhat flat- 
tened, soon divided into several almost cylindrical branches ; 
