AND DEVELOPMENT OF PYROSOR1 A 195 
I recognize an ovisac. Lesueur describes it as one of the 'oeufs' or foetuses, which are 
well represented in figs. 8-11. 
Contemporaneously with Lesueur*, that great, but unfortunate anatomist, Savigny, 
directed his attention to the Pyrosomata, the peculiarities of whose structure found, at 
length, an adequate expositor in him; and his account of the anatomy of Pyrosoma 
gigauteum is at once so lucid and so concise, that I cannot do better than reproduce it, as 
an introduction to my own memoir. 
The subjects of Savigny's observations were obtained at Nice by Ilisso, and by him sent 
to Cuvier. 
"This Pyrosoma (P. gigauteum) is a large cylindrical tube, composed of a gclatinons 
transparent substance, closed and rounded at one end, at the other, truncated and pro- 
vided with an aperture narrowed by an annular diaphragm, which is not without analogy 
with the membranous circle of the BolrylUdcv. 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 tin 
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 enlargements, which corre- 
spond with the conical eminences of the external surface 1 , and which are likewise pierced 
at their apices. The latter apertures, similar to the foregoing both in 1 in and number, 
are situated opposite the anus, and give exit to the faces. 
"This diametrical opposition of the orifices of its cells is a novel peculiarity of tin 
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 natu- 
rally inclined to think that in this genus, as in the foregoing f, it is the most prominent 
orifice which transmits the food to the pharynx and which admits the water requisite for 
the branchiae. 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 late- 
rally, 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 pro- 
jection which the cell makes externally, and whose orifice is provided with a festooned 
The second memoir of the second part of the celebrated « Memoires sur les Animaux sans Vertehres, » entitled 
" Observations sur les Alcyons a deux oscules apparens, sur les Botrylles, et sur les Pyrosomes," bears the inscription, 
" Lues a la premiere classe de l'Institut le 1 CT Mai 1815;" with the note, " Ce memoire a e'te present le 1 7 Avril ; 
mais les travaux de la classe en ont fait diffe'rer la lecture." 
t [viz. Botryllm.] 
2 d 2 
