1869.] DR. J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. 75 
and effete fluids of the animal are on the same principle as artery and 
vein in the higher animals, the excurrent canals having their minute 
origins near the terminations of the incurrent canals. But this dis- 
tribution of the two systems does not obtain in all massive sponges. 
In some species of symmetrically oval or nearly spherical forms we 
find a modification of the system that obtains in the cup-shaped 
sponges, the inner portion of the cup being replaced by a large cen- 
tral cloacal tube into which the effete streams from the sponge are 
poured, and from the mouth of which they are projected, in many 
cases with a considerable degree of force. 
This system is well exemplified in the genus Grantia. 
Among the siliceo-fibrous sponges, we recognize the same principle 
in Iphiteon beatriz (Aphrocallistes beatriz, Gray), which in every 
other peculiarity of its skeleton is truly an Iphiteon. This variation 
in its habit from the cup-shaped siliceo-fibrous sponges is not sufficient 
to constitute it a separate genus, as we frequently find in the same 
species of sponges (as in Halichondria panicea) that one individual is 
massive with simple surface-oscula, while larger specimens, in addi- 
tion to the surface-oscula, have several large cloacal appendages, re- 
ceiving the excurrent streams in their cavities and discharging them 
from a common orifice. Such modifications of the excurrent sys- 
tem prevail to a very considerable extent in many other sponges ; 
but the typeof the skeleton-structure, which should always form 
the basis of generic characters, is never found to vary under any 
circumstances. 
The descrimination of the genera and species of the siliceo-fibrous 
sponges is by no means a difficult task if we address ourselves to the 
operation with a sufficient degree of care and attention. 
In our determination of genera it is necessary that the skeleton- 
structures should be examined in sections parallel to the surface of 
sponge, as well as in those at right angles to it, as the general aspects 
of these two sections are essentially different. Thus in Iphiteon 
callocyathes a section of the skeleton at right angles to the confluent 
radial strata presents no appearance of the rotulate arrangements of 
the fibre that are so characteristic of the genus; and in Myliusia 
the crypt-like form of the skeleton is only distinctly visible in a sec- 
tion at right angles to its surface. 
The most efficient and striking specific characters are to be found 
in the expansile dermal system, in the spicula of the dermal mem- 
brane, and in the peculiarities of the structure of the connecting 
spicula, The characters derivable from the skeleton-fibre are often 
very effective ; but in several of the species they so closely resemble 
each other as to be relatively of very little value as distinctive cha- 
racters, while in no two of the known species of siliceo-fibrous sponge 
have we ever seen the same forms of connecting spicula and spicula 
of the dermal membrane occurring together. In the discrimination 
of species we should especially note the peculiarities of this interest- 
ing and beautiful dermal organism; and a portion of it should be 
boiled in nitric acid to obtain the spicula contained in it in a sepa- 
rate state. 
