Mr. W. Clark on the genus Lepton. 129 



fibres ; resembling exactly the embryonic muscular fibres of the 

 frog described by Kolliker. The larvse in which I observed this 

 belonged to a very peculiar small Cynthia, in the Collection of 

 the British Museum. Contrary to the usual course, the larvse 

 had attained a very considerable degree of development in the 

 space between the inner tunic and the outer wall of the branchial 

 sac, and had so become preserved with their parent. 



Another point of great interest about the larvse may be men- 



ioned here. The integument of the tail and of the hody of young 



TvcB, in which the body contains nothing but a mass of cells, and 



'ers no trace of any organs or apertures, presents clear and un- 

 istakeable signs of the presence of cellulose. The determination 

 of this point is one of the desiderata left by Lowig and Kolliker 

 (Annales des Sciences, 1846), and it shows, I think, very clearly 

 that the Ascidians do not necessarily get their cellulose, as they 

 suppose, from the Diatomacece or other ingesta. Do the cells of 

 the tail of the foetal Ascidian secrete cellulose as the " Primordial- 

 schlauch " in plants secretes it ? If so, they must fix carbon ; and 

 the physiological distinction between animals and plants will 

 disappear, as the anatomical ones have already disappeared. 



In referring to the analogies between the Salpce and Doliolum, 

 Dr. Krohn appears to uphold the doctrine of the fundamental 



fference between the Salpa and other Ascidians. In the me- 



oirs referred to, I have endeavoured to show, on the contrary, 



at there is but one type of Ascidian structure, and that the 

 fariations upon this type pass insensibly into one another. Sub- 

 uent investigations, which I hope to make public at no distant 



riod, have to my mind demonstrated the truth of this propo- 

 ition. The great difficulty I have found among the Ascidians 



s been, indeed, to discover any good anatomical distinctions 



ong the genera. 



DESCRIPTION OF PLATE III. B. 



1 . Doliolum M'dlleri, asexual individual, from the ventral side : a, gem- 

 miferous tube or " gemmariura ;" b, penultimate muscular band 

 with its ends inserted into the gemraarium. 



2. Larva of D. Nordmanni : c, larval tegument ; d, young Doliolum ; 

 e, vesicular appendage ; f, axis of the tail. 



3. The same further developed and more magnified. Letters as before. 



XIV. — On the genus Lepton. By William Clark, Esq. 

 To the Editors of the Annals of Natural History. 

 Gentlemen, Exmouth, July 5, 1852. 



I HAVE stated in the July 'Annals' for 1852, that the discovery 

 of the animal of the Lepton convexum has put it in my power to 

 Ann. ^ Mag. N. Hist. Ser. 2. Vol. x. 9 



