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. Is one 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. 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 Fyrosoma, 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, piiblished 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." 



Fig. 9 represents, in fact, an ovisac with a segmented blastoderm, Avhile in fig. 10 the 

 ' five young ' are the cyathozooid and the fom* 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 lies in the 

 same place as that in which I have always found it, viz. in the large mid-atrium and 

 altogether behind the intestine. M. Yogt 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. 



" This incubation, perhaps, takes place only during certain periods of the year, or of 

 the life of the zooid, whence the incubatory cavity is found only in some individuals and 

 not in all. The formation of ova in the projecting ovary would continue for a certain 

 time. The ova would pass, as they became fecundated, into this incubatory cavity, would 

 develope there, and would iiltimatcly be set free to lead an independent existence. 

 Perhaps, indeed, the incubatory sac may be thrown off bodily, and thus give rise to the 

 base of the new cylinder." {I. 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 renemng my 

 investigations which I desired, but little expected, was unexpectedly afforded me. In 

 October of the year 1859, Rear-Admiral EitzRoy, F.R.S., the indefatigable Superin- 



* " Recherches sur les Animaux inferieurs de la Mediterranee," Mem. de I'lnstitut National Geuevois, torn, ii., 1854. 



