106 Dr Grant’s Observations on the Structure and 
dust ; while in the Spongia panicea and Spongia cristata , it con- 
sists of larger flocculi of a dark-grey membranaceous substance. 
The streams likewise convey from the interior of the animal, 
along with the excrements, certain soft, round, small bodies, ge- 
nerally of an opaque yellow colour, which are distinctly seen 
disseminated through the whole texture of most marine sponges, 
and which, for the present, we shall consider as the ova. The 
round apertures may, therefore, without impropriety, be termed 
fecal orifices , in order to distinguish them from the pores of a 
very different nature, which are destined to transmit water into 
the interior of the body. 
The fecal apertures are raised to the extremities of projecting 
papillae, in such sponges as cover the sides of rocks, in order to 
convey the excrements beyond the pores and general surface of 
the animal. In the Spongia oculata , Spongia palmata , Spon- 
gia ccerampelina , and such branched species as have a soft downy 
surface, the fecal orifices are ranged in close order along the 
outer margins of the branches, and very few are observed on 
the flat surface, in order to prevent the excrement from falling 
in the direction of the flat woolly surfaces, which would be very 
apt to retain it, and thus choke up the groups of pores which 
are seen every where over their surface. Such branched sponges 
have not, and do not require, projecting papillae, because they 
hang suspended by a narrow stem, and are kept sufficiently 
clean by receiving gentle undulations from the constant motions 
of the sea. The same applies to the soft downy white Spongia 
compressa , which always hangs down, and whose orifices are 
always marginal. The bright yellow porous placentiform mass 
of the Spongia panicea has no papillae ; indeed the fecal orifices 
are sometimes even lower than the general surface of the animal, 
and I have never seen this sponge, excepting on the under sur- 
face of rocks, with its orifices perpendicularly downwards ; so 
that the excrements fall clear of its surface by their own gravity, 
without the assistance of papillae. The flat species which are 
found encrusting Fuci, Sertulariae, Corallines, or other moveable 
bodies, have very seldom prominent papillae, because they are 
cleansed by the agitations of the sea like the branched sponges. 
What relates to the cleanliness of their surface applies equally 
to their means of receiving food ; for it is only in proportion to 
