ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA = 32E 
18-25, increasing by degrees from the first, reckoning from the top, to 
the fifth or even the eighth; longitudinal vessels 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 Pyrosomea atlanticuin, has a conical body 
6 or 7 inches long, with its external protuberances terminating in 
subulate points, and inhabits the equatorial seas. 
Mr. F. D. Bennett exhibited some specimens of Pyrosoma at a 
meeting of the Zoological Society on the 25th of June, 1833, and gave 
an account of their phosphorescence. <A paper by the same author, 
“On marine Noctdluce,” 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 cloacal aperture is capable of contraction. 
In the ‘Comptes Rendus’ for 1840 (tom. x. p. 285), M. Milne- 
Edwards published some important observations on the circulation of 
the Pyrosomata, by which he not only demonstrated, 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. With 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 Pyrosoma has been published since 
Savigny’s time, except my own memoir “On the Anatomy and 
Physiology of Salpa and Pyrosoma, together with remarks on 
Doltolum and Appendicularia,’ contained in the ‘ Philosophical Trans- 
actions’ for 1851. 
In this memoir I have detailed the results of investigations, made 
under difficult circumstances and with but a few hours at my disposal, 
upon a single specimen of what I suppose to have been Pyvrosoiza 
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 common 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 
VOL, IT Y 
