8i 



of the pericardium, which woukl propcl the blood throuoh the cjlomeruH and along Masterman's 

 ventral sinus (which is said to underlie the notochord) to the front border of the mouth, 

 travelHno- round the sides of the mouth throu^h the two vessels described in that position by 

 Masterman. These may be continuous witli the oral sinus of which I have obtained some 

 evidence in C. levinseni. The course of the blood, as thus suggested, would be in agreement 

 with the course which has been described by Spengel in Balanoglossus. 



The antcrior ventral vessel of the body and stalk can be traced as far as the septum 

 between the second and third body-cavities, or in one case [C. levinseni, PI. X, fig. 124) even 

 into the incomplete ventral mesentery of the collar. It appears to me probable that this ventral 

 vessel in some way receives a part at least of the blood coming from the collar, and conveys it 

 to the stalk by the vessel running on the anterior side of this structure. After having traversed 

 the entire length of the stalk, it may be supposed that the blood returns by the posterior stalk- 

 vessel to the wall of the second stomach where, in C. gracilis at least (figs. 22, 71) it appears to 

 end in a dilated structure which is probably muscular. This may have the function of propelling 

 the blood through the sinuses of the stomach and so of enabling it to reach the origin of the 

 dorsal vessel. It is, however, possible that it acts in exactly the opposite direction, and that 

 the posterior vessel is the afferent vessel of the .stalk. 



If there be anything in this entirely tentative scheme of the circulation it may be noted 

 that the force of the beat of the pericardium would appear to be largely of importance in 

 driving the blood through the stalk. In the long-stalked forms {C. gracilis and C. sièogae) there 

 must be a considerable amount of resistance to be overcome in this region ; and it may further 

 be remembered that the stalk requires an efficiënt nutritive arrangement, not only to supply its 

 strongly developed muscles, but also for the growth of the buds which are produced so profusely 

 from the basal end of the stalk in these species. 



XV. REPRODUCTIVE ORGANS. 



The zooids of C. dodecalophus appear to be without e.xception female. As all the previous 

 literature of the genus refers to this species, it follows that the male organs have not hitherto 

 been described, although I have alluded to the males of C. sièogae in Vol. VII of "The 

 Cambridge Natural History" (04, p. 26). The only previous accounts of the male organs of 

 the Pterobranchia refer to Rhabdopleura, and are represented by Lankester's observation 

 (84, p. 633) that a single testis occurs on the right ') side of the intestine, opening to the 

 exterior near the anus, its blind end in some cases projecting beyond the part of the body- 

 wall which contains the loop of the alimentary canal ; and by the remarkable statements of 

 CoNTE and Vaney (02, i), to which I shall refer later. 



The material at present under consideration consists of female colonies of C. dodecalophus, 

 C. levinseni and C. gracilis and a male colon\- of C. sibogae. 



i) Lankester's fig. 7 (PI. XL) shews the testis on the left side, as indicated in the explanation of the Plates (p. 645). The 

 figure is perhaps reversed. 



SIBOGA-EXrEDITIE \\\'l/'is. " 



