REPORT ON THE TUNICATA. 



101 



it by which water enters to the body of the Appendieuhiriaii and [lasses from it 

 (sec arrows Fig. 12). 



Fic. 13. — Diagram of Append icularia from the right side. (From the Eiicycloii.-cJia Britannica, 'Jth eil.) 



a. anus; app. tail; at. one of the atrial apertures; f>r. brnncliial aperture; hr.s. brancliial sac; d.t. dorsal tubercle; 

 end. endostyle ; h. heart; ('. intestine; iii. muscle band of tail; n. nerve cord in body; n.' nerve cord in tail ; 

 7i.fj. large anterior (cerebral) ganglion; ii.fi.' caud.al ganglion; ii.f/." enlargement of nerve cord in tail; 

 a\ cesophagus ; ot. otocyst ; or. ovary ; p.p. peripharyngeal band ; Sff. one of the stigmata ; s.o. oral sense-organs ; 

 St. stomach ; tes. testis ; n. urochord ; '/'.' its cut end. 



The branchial aperture or mouth is at the ante'rior end of the 1)0(1}% and leads into 

 a branchial sac or pharynx whirh presents for notice only an endostyle, pcripharynoeal 

 bands, and two ciliated openings into tubes leading to the exterior. There are no 

 tentacles, no dorsal lamina or languets, and no systems of vessels. The endo.stylc is 

 very short, only reaching one-third or halfway along the ventral edge of the sac. The 

 peripharj'iigeal bands run from the anterior ventral part of the sac obliquely backwards 

 and dorsally, so as to reacli the dorsal middle line near the posterior end of the sac 

 (see Fig. 13,^^.^.). 



The two ciliated openings (often called stigmata) are placed far back in the branchial 

 sac, one at each side of the mid-ventral line. These openings correspond not to the 

 stigmata of ordinary Ascidians, such as the species of Aacidia, Ijut to the primar}- 

 stigmata which first appear in the larva, and, according to Yan Beneden and Julin, to 

 the internal openings of the gill- clefts in Amphioxus and the Vertebrata. The tubes 

 from the ciliated openings run ventrally, and open independently to the exterior in 

 front of the tail and behind the anus (see Fig. 13, at). These tubes correspond to the 

 right and left atrial involutions of the epiblast, which in ordinary Ascidians fuse dorsally 

 to form the peribranchial cavity. The Larvacea therefore in this respect also possess a 

 character which is only a temporary stage in the development in other groups of the 

 Tunicata. 



At its posterior end the l>ranchial sac narrows to become continuous witli tlic 

 cesophagus, which curves posteriorly and ventrally to enter the large and sometimes 

 bilobed stomach. The intestine (except in the case of Fol's remarkable Koivalevshia 



