34 



PHYLUM TUNIC ATA (UROCHORDA). 



large vas deferens ; gemmation from post-abdomen which has the heart 

 at its extremity. 



The post-abdomen contains the epicardium, which divides it into a right 

 and left portion, the heart and pericardium, and in its upper part the gonads 

 (Fig. 26). The pericardium (19) is U-shaped and contains the heart (also 

 U-shaped) in its posterior part. The epicardium (17} bifurcates in front 

 into two tubes which abut against the pharynx but do not open into it in 

 the adult ; posteriorly it bifurcates so as to grasp the 

 bend of the pericardium (20). Budding is effected by the 

 separation of the post-abdomen from the abdomen and its 

 fission into pieces (Fig. 27). The portion of the heart and 

 pericardium in each piece atrophies and the epicardium 

 develops in the usual way into pharynx, atrium and intes- 

 tine of the bud. In Amaroucium, and possibly others, 

 budding takes place in the summer ; towards winter this 

 ceases and sexual organs are formed. The budding zooid 

 regenerates a new post-abdomen. This method of bud- 

 ding is clearly of the stolonic kind, such as we find in 

 Clavelina and Distomidae, differing only by the presence 

 of the heart in the stolon. 



With intestinal loop twisted and generally smooth-walled 

 stomach. 



Polyclinum Sav, (Fig. 26). Systems simple, stomach 

 smooth- walled, most seas. Glossophorum Lahille, hori- 

 zontal membranes of pharynx denticulated, each colony 

 of a single system ; Med. Aptogaster Herd., Polyclinoides 

 v. Drasche, Aplidiopsis Lahille, with non-twisted intes- 

 tine and smooth-walled stomach ; Med., Atl. Pharyngo- 

 dictyon Herd., pharynx with simple 

 meshwork of rectangular meshes, fine 

 longitudinal bars supposed to be ab- 

 sent (see p. 11); Antarctic, 1,600 

 fms. ; Tylobranchion Herd. 



Intestinal loop not twisted, wall of 

 stomach grooved or areolated. 



Apilidium Sav., without languets, 

 most seas. Psammapilidium Herd. 

 Amaroucium M.-Edw. (Amaroecium) 

 (Fig. 27), atrial aperture with a lan- 

 guet, post-abdomen not separated off 

 by constriction, most seas. Sigillina 

 Sav., .FVa<7nwwGiard and Fragaroides 

 Maur., with 8 buccal lobes, Med. Sid- 

 nyum Sav., 6 buccal lobes, areolated 

 stomach ; N. and S. Atl. Morchellium Giard. Synoicum Phillips, each 

 colony forms a separate club-shaped mass. Parascidia M.-Edw. Cir- 

 cinalium G-iard. Morchellioides Herd. Polyclinopsis Gottschaldt. 



Fam. 4. Didemnidae. Colony usually thin, and encrusting, rarely 

 thick, never stalked ; systems irregular, inconspicuous or absent, common 

 cloacal apertures usually conspicuous ; zooids placed perpendicularly or 

 obliquely to surface, divided into thorax and abdomen ; mouth 6-lobed, 

 atrial opening plain or with atrial languet ; test usually with stellate cal- 

 careous spicules ; ectodermal processes well developed, with muscles which 



FIG. 27. Amaroucium showing seg- 

 mented post-abdomen, x, y buds, 

 k anterior swollen end of epicardium 

 in the bud (after Kowalevsky). 



