REPORT ON THE TUNICATA. 



129 



colonies. The Ijuds would be formed as processes of the body-wall containing pro- 

 longations from a blood sinus filled with undifferentiated mesodermal cells and having a 

 median process probably continuous with the endoderm of the branchial sac' A slight 

 modification of this process would result in the formation of a gemmiparous stolon witli 

 contained blood vessels, and an epicardial partition such as is now found in the case of 

 Clavelina and Perophora where permanent colonies are produced, while a degeneration 

 of the same apparatus for budding would result in the formation of rudimentary 

 vascular projections from the body like those which exist in varied conditions in the 

 test of Ciona, Corella, and other Ascidiidfe." 



This ancestral form (E. in table, p. 120, or p. 150), which may be called a Proto- 

 ascidiate, was probaljly slightly elongated antero - posteriorly, and attached by the 

 posterior end, l)ut not pedunculated (Fig. 18). The stomach and intestine were placed 

 posteriorly to the branchial sac, and the terminal part of the intestine, on account of 

 the anterior position of the atrial aperture, was Ijent forwards so that the alimentary 

 canal as a whole formed a narrow loop. 



From this point (E.) in the table at least three ancestral lines started. The 

 first leads wdth very little change to Clavelina (Fig. 19), where the body is 



S 



Fig. 19. — Colony of Clavelina. 



B. bud; at, atrial aperture ; 6?'. branchial aperture ; 6r.s. branchial sac ; en. endostyle ; i. intestine; m. mantle; 

 n.p. nerve glanglion ; a*, oesophagus ; )•. rectum ; s. stolon ; st. stomach ; t. test. 



considerably elongated and more or less pedunculated, while permanent colonies are 

 produced — usually by means of a ramifying stolon. In Clavelina j^'^oducta, Milne- 

 Edwards,^ however, a more primitive condition is found, the stolon being scarcely 

 developed, and the buds being usually produced from the posterior part of the body of 

 the parent Ascidian. 



^ See Van Benedcn and Juliu, Morph. A. Tuniciers, pp. 289 et seq. 



- See Herdman, On the Evolution of the Blood-vessels of the Teat in the Tunicata, Nature, vol. xxxi. p. 247, 1885. 



^ il/e'm. Acad. Sci. Paris, torn, xviii. p. 217, 1842. 



(ZOOL. CHALL. E.XP. PART LXXVI. — 18SS.) Gggg 17 



