79 



homology. He is apparently induced to reject Masterman's interpretation by finding that the 

 central or posterior tube oi the stalk. is "coiitinuous with the lining of the alimentary canal". 

 The proof of this last statement is not given by Fowler, and I think it more probable that the 

 relation of the ijosterior tube to the alimentary canal is of the kind indicated in figs. 22 and 

 7 1 for C. gracilis. Fowlkr supposes that the central tube is endodermic, and I imagine that 

 his view of the budding is that it behaves in somewhat the same way as the epicardium of a 

 Tunicate. But there is no evidence that this is the case, and the account given by Masterman 

 (98, 2) of the budding of Ccphalodiscïts is distinctly opposed to Fowler's view. There can be 

 little doubt that the same interpretation of the structures in question applies to the two genera; 

 and it appears to me probable that in both cases the stalk is provided with an anterior and 

 a posterior limb of a loop-like ventral vessel, the posterior limb terminating on the wall of the 

 alimentary canal. 



P e r i c a r d i a 1 sinus o r h e a r t. 



The pericardium and pericardial sinus form a conspicuous feature of all specimens that 

 are sufficiently well preserved. The pericardium {per.) has precisely the same relations as those 

 of the same organ in Balanoglossus (the " Herzblase") as described by Spengel (93, p. 505). 

 It is well shewn in Masterman's most recent paper (03, figs. i — 8), and is illustrated by 

 PI. XIII, figs. 181, 182, 173; PI. XI, fig. 138, PI. IV, figs. 33, 37 of the present Report. 

 It is in contact with the tip of the notochord (fig. 33) and lies immediately beneath the central 

 nervous system. The proboscis-pores open into the anterior body-cavity between its lateral walls 

 and the dorsal horns of the collar-cavity (figs. 112, 137, 138). The posterior wall of the 

 pericardium is invaginated, the space thus formed (heart) having the same relation to the 

 pericardium that is found in the Tunicata (cf. Ritter, 02, i). Spengel (93, pp. 506, 625) has 

 given reasons for believing that in Balanoglossus the pericardium, although not in itself a 

 vascular space, may be regarded as functionally a part of the vascular system, since the blood 

 in the heart is propelled by the rhythmical contractions of the pericardium — contractions 

 which are well known to occur in Tornaria. The identity of the relations of the pericardium 

 to other organs in Enteropneusta and Cephalodiscus makes it highly probable that what is true 

 of the former is also true of the latter. 



The pericardium in Cephalodisais is developed at a very early stage in the buds, and 

 is further considered in Section X\T. 



I come now to those parts of the vascular system which I regard as less certainly 

 proved to exist. Among these are the "vessels" described by Masterman in the immediate 

 neighbourhood of the pericardium and notochord. I do not feel myself in a position either to 

 a.ssert or to deny the e.Kistence of these vessels, though I regard it as highly probable, on a 

 priori grounds, that they do exist. I have indicated above (p. 74) the general nature of 

 Masterman's results with regard to these particular vessels. 



Although I have devoted a considerable amount of attention to the region in which 

 the dorsal vessel terminates in front, I have found but little evidence which appears to me 



