316 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
The subjects of Savigny’s observations were obtained at Nice by 
‘Risso, and by him sent to Cuvier. 
“This Pyrosoma (P. giganteun) is a large cylindrical tube, com- 
posed of a gelatinous transparent substance, closed and rounded at 
one end, at the other, truncated and provided with an aperture 
narrowed by an annular diaphragm, which is not without analogy 
with the membranous circle of the Botryllide. The surface of the 
tube presents conical and smooth eminences of different sizes, some 
simple and very short, others longer and terminated by a lanceolate 
piece. Each eminence is pierced at its apex, behind the base of the 
lanceolate piece, when this exists, by a little circular hole, surrounded 
by a brown and projecting edge. This aperture, in my opinion, 
serves to give entrance to the water, and leads into the pharynx. 
“The inner wall of the tube presents slight hemispherical enlarge- 
ments, which correspond with the conical eminences of the external 
surface, and which are likewise pierced at their apices. The latter 
apertures, similar to the foregoing both in form and number, are 
situczted opposite the anus, and give exit to the feces. 
“This diametrical opposition of the orifices of its cells is a novel 
peculiarity of the Pyrosoma, and determines the form of the whole 
body. The functions of each of these orifices seem to me to be 
sufficiently indicated by their relative position. One is naturally 
inclined to think that in this genus, as in the foregoing, it is the most 
prominent orifice which transmits the food to the pharynx and which 
admits the water requisite for the branchize. Besides this, the water, 
incessantly renewed at the outer surface of the tube, could not be so 
rapidly or completely changed in its interior. The arrangement of 
the viscera in each animal agrees with this first indication. 
“To describe the animals of the Pyrosoma, we may suppose the 
cylinder to be placed vertically on its base—I mean, on its rounded 
and closed end ; for the opening of this body is evidently its summit. 
Each animal then represents an elliptical sac, compressed laterally, 
whose great axis is horizontal, and consequently perpendicular to that 
-of the cylinder. This sac, formed by a delicate and transparent tunic, 
is attached to the cell which contains it, only by the circular opposed 
-apertures of its two ends. The extremity which is turned towards 
the axis of the cylinder is simply rounded : that directed towards the 
circumference is prolonged into a neck, whose length is proportional 
to the projection which the cell makes externally, and whose orifice 
is provided with a festooned membrane. The lower edge of the sac 
exhibits the same brown and undulating vessels as the back of the 
lV tviz. Botryllus.) 
