AND DEVELOPMENT OF PYROSOMA. 199 



" except upon tlie diaphragm which surrounds the aperture." The tunic is provided 

 "helow the abdomen with two transverse muscles, and, besides, is marked by interlacing 



muscular nervnres, 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. 



" Branchiee wholly separated behind, divided in front as far as their bases, rounded or 

 acuminated at their apices ; transverse vessels 18-25, increasing by degrees from the fii-st, 

 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 Pyrosoma atlanticum, has a conical body 6 or 7 inches long, 

 with its external protuberances terminating in subulate points, and inhabits the equato- 

 rial seas. 



Mr. P. 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 their phosphorescence. A 

 paper by the same author, " On marine Noctihicce," printed in the ' Proceedings ' of 

 the Zoological Society for 1837, contains further remarks on the same subject, and the 

 statement that the ' sphincter-hke ' membrane which surrounds the cloacal aperture is 

 capable of contraction. 



In the ' Comptes Bendus ' for 1810 (tom. x. p. 285), M. Milne-Edwards published some 

 important observations on the circulation of the Pyrosomata, 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. 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 Boliolum and. Apj^endicularia," contained in the ' Philosophical Transactions ' 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 Pyrosoma atlanticum. 



By the publication of this essay there was added to vrhat 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 ; 



