200 PROFESSOR HUXLEY ON THE ANATOMY 
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 com- 
pound embryos were observed in this specimen, however ; and hence I have always felt a 
great desire to re-examine Fyrosoma, for the purpose of ascertaining the real nature and 
origin of such singular bodies. Prom 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 Tyrosoma, 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 pi. 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. 9 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 
»» 
lies 
Pig. 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 foetus. 
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 especially as in fig. 9 it 
same place as that in which I have always found it, viz. in the large mid-atrium and 
altogether behind the intestine. M. Vogt concludes by putting forward the hypothesis 
that the ova pass down the canal of the ovisac into the neighbourhood of the intestine, 
where an incubatory cavity, in which their final development takes place, is formed for 
them in the thickness of the inner tunic. * , f 
" This incubation, perhaps, takes place only during certain periods of the year, or o 
the life of the zooid, whence the incubatory cavity is found only in some individuals an 
not in all. The formation of ova in the projecting ovary would continue for a certam 
time. The ova would pass, as they became fecundated, into this incubatory cavity 
develope there, and would ultimately be set free to lead an independent existence. 
Perhaps, indeed, the incubatory sac may be thrown off bodily, and thus give rise to 
base of the new cylinder." (L c. p. 90.) 
These observations and suggestions obviously leave much room for further inquiry, 
and my satisfaction will be easily understood when that opportunity of renewing niy 
ould 
gations which I desired, but little expected, was unexpectedly afforded me 
In 
October of the year 1859, Rear-Admiral PitzBoy, P.H.S., the indefatigable Superin 
* " Recherches sur les Animaux inferieurs de la Mediterranee 
1854. 
