AND DEVELOPMENT OF PYROSOMA. 
199 
"except upon the diaphragm which surrounds the aperture." The tunic is provided 
" below the abdomen with two transverse muscles, and, besides, is marked by interlacing 
muscular nervures, which are very fine, and hardly visible with a strong lens The 
festooned membrane at the entrance of the branchial sac would' be exactly circular if its 
posterior and inferior edge were not prolonged into a point. 
" Branchiae wholly separated behind, divided in front as far as their bases, round* I or 
acuminated at their apices ; transverse vessels 18-25, increasing by decrees from the fh>t, 
reckoning from the top, to the fifth or even the eighth ; longitudinal vess Is 11-17, the 
middle one only reaching the first transverse vessel, the following on each side attaining 
the second, and so on, the most external vessels being the shortest of all." 
The other species, or the Fyrosoma atlanticum, lias a conical body G or 7 inches long, 
with its external protuberances terminating in subulate points, and inhabits the equate- 
rial seas. 
Mr. F. D. Bennett exhibited some specimens of Fyrosoma at a meeting of the Zoological 
Society on the 25th of June, 1833, and gave an account of iheir phosphorescence. A 
paper by the same author, "On marine Noctilucce" printed in the ' Proceedings ' of 
the Zoological Society for 1837, contains further remarks on the same subject, and the 
statement that the 'sphincter-like' membrane which surrounds the cloaeal aperture is 
capable of contraction. 
In the < Comptes Bendus ' for 1810 (torn. x. p. 285), M. Milne-Edwards published some 
important observations on the circulation of the Fyrosoma ta, by which he not only de- 
monstrated, for the first time, the existence of a heart, but proved that in these, as in most 
other Ascidians, this organ is subject to a regular reversal of its peristaltic contractions. 
The regular movement of the branchial cilia is also noted in this communication. Wit h 
the exception of this valuable contribution to our knowledge of the genus, I am not 
aware that, with the exception of M. Vogt's short paper, to be noticed below, any account 
of observations on Fyrosoma has been published since Savigny's time, except my own 
memoir "On the Anatomy and Physiology of Salpa and Fyrosoma, together with remarks 
on Doliolum an&Ajypendicularia" contained in the ' Philosophical Transactions ' for 1851. 
In this memoir I have detailed the results of investigations, made under difficult 
rcumstances and with but a few hours at my disposal, upon a single specimen of what 
suppose to have been Fyrosoma atlanticum. 
By the publication of this essay there was added to what had been already made known, an 
account of the tubules which envelope the intestine, and open into the stomach by a com- 
mon axis. The lateral circular palettes, called ' ovaria ' by Savigny, were shown not to have 
the function assigned to them. The blood was stated to be contained in one great sinus 
which extends through the whole of the body ; and the reversal of the motion of the heart, 
observed by Milne-Edwards, was confirmed. The ' four undulating vessels ' of Savigny 
were shown to be the expression of an endostyle, such as exists in other Ascidians. It 
was further stated that the edges of the vertical branchial bars, only, were ciliated. The 
ciliated fossa, the peripharyngeal ridges, the languets, and the otoliths were described. The 
' liver ' of Savigny was shown to be the testis ; and the form and mode of development of 
the spermatozoa were described. The characters of the female organs were determined ; 
I 
