Mr. T. H. Huxley on the genus Doliolum. 127 



subsequently unfold themselves and project) are visible. Upon 

 the dorsal surface the rudimentary gemmarium had already made 

 its appearance in the form of a conical projection. The young 

 animal was not capable of any independent movement, and its 

 tail was only seen at intervals slightly twitching and vibrating. 



Final Remarks. 



' In the course of the preceding observations, the analogies 

 which connect the genus Doliolum with the Salj)ce have been re- 

 ferred to. These analogies consist not only in the similar mode 

 of life, the similar diametrical opposition of the apertures, and 

 especially in the similar muscular apparatus of each, but also, as 

 I have endeavoured to show, in the similar mode of propagation, 

 according to the laws of the Alternation of Generations, by 

 which, as in the Salpce, sexual and asexual generations occur in 

 regular succession. Yet, in the genus Doliolum the typical cha- 

 racters by which the Ascidian is separated from the Salpa pre- 

 dominate; such are distinctly seen in the absence of the respi- 

 ratory siphon, in the structure of the respiratory apparatus, and 

 in the metamorphosis. 



By their approximation to the Salpce, and by the simpler struc- 

 ture of their branchise, however, Doliolum seems to me to stand 

 lower than the Compound Ascidian s ; although, like the higher 

 Ascidians, it is solitary, and, unlike them, it is free. 



The Ascidians then, according to their mode of life, may be 

 divided into fixed and free. To the former belong the numerous 

 genera of simple and compound or aggregated Ascidians, to the 

 latter the solitary genus Doliolum and the aggregate genus 



rosoma. 



Note by the Translator. 



Dr. Krohn does not appear to have met with a memoir upon 



oliolum and Appendicularia ( Vexillaria) published in the ' Phi- 

 losophical Transactions ' for 1851. I have there described and 

 figured D. denticulatum, and I am delighted to find that in all 

 essential points, what I have stated is confirmed by one of the 

 most accurate and careful of the German observers. 



Dr. Krohn does not seem to have been more successful than 

 myself in making out the ovaries of Z). denticulatum ; but I should 

 hardly be inclined to adopt his supposition, that this species, in 

 opposition to its immediate congeners, is dicEcious ; the explana- 

 tion 1 have suggested {loc. cit. p. 601) seems to me still to be the 

 more plausible. 



It will be observed that Dr. Krohn considers what I have 

 called the testis to be the vas deferens, and vice versd. I feel quite 



