216 THE VOYAGE OF H.M.S. CHALLENGER. 



hisgreal work on the Compound Ascidians, to show that they reproduced by gemmation, 

 all bough Long before Lister ' had pointed out the same fact in another genus of the famdy, 

 /', rophora. 



Milne-Edwards gave a very full account of the anatomy and physiology of Clavelina, 

 and described several species at considerable length. He proposed that Clavelina and 

 Perophora should be separated from the Simple Ascidians, with which up till that time 

 (1842) they had been associated, and he formed for their reception a group, the Ascidire 

 Sociales, intermediate between Simple and Compound Ascidians, and independent of 

 both. 



Griard, in his "Beehercb.es sur les Synascidies," published in 1872, adds little or 

 nothing to Milne-Edwards's account of the genus Clavelina, which he places along 

 with Perophora and the Compound Ascidians, in his Synascidiae. 



Clavelina, is the typical genus of the Clavelinida?, and shows most of the characteristic 

 features of the family in a marked degree. It differs from Perophora chiefly in the 

 relation of the intestine to the branchial sac, and in having a more or less well developed 

 abdomen. From Ecteinascidia it is separated by the total absence of internal longitudinal 

 liars in the branchial sac. 



The two new species of Clavelina discovered during the Challenger expedition differ 

 somewhat from the previously known species of the genus in the external appearance of 

 the colony, as in both cases the individuals are crow T ded together, and the stolons are 

 present merely in the form of a thick mass of test substance continuous with and 

 uniting the posterior ends of the individuals. 



Clavelina oblonga, Herdman (PL XXXV. figs. 6-10). 



Clavelina oblonga, Herdman, Prelim. Rep., Proc. Roy. Soc. Edin., 1579-80, p. 724. 



External Appearance. — The individuals are closely united into a colony by their 

 posterior ends, which form a thick irregular stolon. The shape of each ascidiozooid 

 is irregularly oblong, sometimes club-shaped or more irregular. The anterior end is wide 

 and rounded ; the posterior is generally very narrow. The apertures are sessile, not 

 lobed, and are placed both at the anterior end. 



The surface is smooth, with occasional transverse wrinkles, especially towards the 

 posterior end. The colour is light yellowish-grey, nearly white. 



Length of the body of a single individual, 2 cm. ; breadth of same, 0'6 cm. ; height 

 of the colony, 6 cm. 



The Test is thin, especially at the anterior end ; it is transparent. 



The Mantle is moderately strong. The margins of the apertures are much pigmented, 

 but not so as to form definite ocelli. 



1 Philosophical Transactions for 1834. Part II. 



