AND DEVELOPMENT OF PYROSOMA. 195 



I recognize an ovisac. Lesueur describes it as one of tlie ' 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 Pyroso77ia 

 giganteimi 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 Risso, and by him sent 

 to Cuvier. 



" This Fyrosoma (P. giganteum) is a large cylindrical tube, composed of a gelatinous 

 transparent substance, closed and rounded at one end, at the other, truncated and pro- 

 vided with an aperture narrowed by an annular diaphragm, whicli is not without analogy 

 with the membranous circle of the BotrylUdce. 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 cu'cular 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 Avail of the tube presents slight hemispherical enlargements, which corre- 

 spond 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 situated opposite the anus, and give exit to the faeces. 



" 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 l)e sufficiently indicated by their relative position. One is natu- 

 rally inclined to think that in this genus, as in the foregoing t, 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 Fyrosoma, 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 jn'o- 

 jection which the cell makes externally, and whose orifice is provided with a festooned 



* The second memoir of the second part of the celebrated ' Mdmoires sur les Animaux sans Vertebres, ' entitled 

 " Observations sur les Alcyons a deux oscules apparens, sur les Botr^vlles, et sur les Pyrosomes," bears the inscription, 

 " Lues a la premiere classe de I'Listitut le 1" Mai 1815 ;" with the note, " Ce mt'iiioii'c a etc presente le 17 Avril ; 

 mais les travaux de la classe en ont fait differer la lecture." 



■\ [viz. BotiyUus.] 



2 D 2 



