322 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
Ascidians. It was further stated that the edges of the vertical. 
branchial bars, only, were ciliated. The ciliated fossa, the peri- 
pharyngeal 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; the presence of 
spermatozoa in the duct of the ovisac was observed; and it was 
proved that the so-called ‘simple embryos’ of Savigny are formed by 
gemmation. None of the compound embryos were observed in this 
specimen, however ; and hence I have always felt a great desire to re- 
examine Pyrosona, for the purpose of ascertaining the real nature and 
origin of such singular bodies. From Savigny’s habitual accuracy, I 
had no doubt of their existence and essential correspondence with his 
account; but it seemed impossible that they should be developed in 
the way he describes. 
In his valuable memoir “Sur les Tuniciers nageants de la mer de 
Nice!,’ M. Vogt confirms my account of the structure of Pyrosoma, 
and adds some remarks, which are, unfortunately, very brief, upon the 
foetuses discovered by Savigny, and which I failed to find in my 
specimen. In pl. 10. figs. 9 & 10, some sketches made in 1847, and 
referred to in a passage of the ‘Ocean und Mittelmeer’ of the same 
author, published in 1848, are given. They are thus described at 
p. 89 of the present essay :— 
“In fig. g the ovisac is seen below the testicle, immediately in 
front of the posterior aperture of the body. It has a rounded form, 
and contains an enormous, yellowish-coloured and almost transparent 
ovum, below which again are accumulated oviform masses which 
exhibit a granular vitellus. I could see no further structure in these 
ova; but, I must confess, I did not carry my investigations very far. 
In fig. 10 I have given an outline-sketch of the individual which 
exhibited five young in its ovisac. The latter has a rounded form, 
but is much larger than in the foregoing specimen, and having pushed 
the viscera downwards, it has extended towards the branchial cavity, 
in which it forms a kind of hernia.” 
Fig. 9 represents, in fact, an ovisac with a segmented blastoderm, 
while in fig. 10 the ‘five young’ are the cyathozooid and the four 
ascidiozooids of a young fcetus. 
I do not understand how the ovisac in M. Vogt’s specimen can have 
occupied the position in which it is figured in fig. 10, the more 
1 “Recherches sur les Animaux inférieurs de la Méditerranée,’ Mém, de l'Institut 
National Génevois, tom. ii., 1854. 
