Mr. W. Clark 07i the genus Lepton. 129 



fibres ; resembling exactly the embryonic muscular fibres of the 

 frog described by KoUiker. The larvae 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 larvae 

 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 larvae may be men- 

 tioned here. The integument of the tail and of the body of young 

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

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

 mistakeable signs of the presence of cellulose. The determination 

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

 (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 Diatomacea 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. -a 



In referring to the analogies between the Salpce and Doliolunt', 

 Dr. Krohn appears to uphold the doctrine of the fundamental 

 difference between the Salpce and other Ascidians. In the me- 

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

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

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

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

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

 sition. The great difficulty I have found among the Ascidians 

 has been^ indeed, to discover any good anatomical distinctions 

 among the genera. 



DESCRIPTION OF PLATE III. B. 



Fig. 1 . DoUolum Miilleri, asexual individual, from the ventral side : a, gem- 

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

 with its ends inserted into the gemmarium. 



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

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



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



— — lju:»^j[ r^fiJi-'^^o l i g 



XIV. — On the genus Lepton. By William Clark, TTsq.; 

 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 .|Ojj 

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



