PLATE VL 



C. gracllis. 



Fig. 60. — Frontal section through arms and dorsal lobe of proboscis. All the arms appear in the section 

 except the fourth left arm. 



Fig. 61. — A more ventral section of the same specimen, cutting the dorsal edge of the metasome, with 

 the two oviducts [ovd.). The grooves of the ten arms are indicated: — op.r., right lateral lobe 

 of operculum. 



Figs. 62 — 70. — Frontal sections of another individual in which the ventral lobe of the proboscis is turned 

 forwards, as in fig. n- The arrangement of the arms and operculum was made out with the 

 aid of a plasticine reconstruction. 



Fig. 62. — Through the proboscis-stalk, in front of the beginning of the collar: — per., pericardium, 

 ventrally to which are seen the two principal groups of proboscis-muscles {nis.p). 



Fig. 63. — Through the proboscis-stalk, in the region of the proboscis-pores [p.p.), and the tips of the 

 anterior horns {b.c.-a.) of the collar-cavities. 



Fig. 64. — Through the notochord [nch.). The second left arm is directed ventrally from its base (somewhat 

 as in the case of R. i in fig. 32), which is thus represented only by a part of the food-groove. 

 The arm curves forwards later, so that it is cut near its tip in fig. 63 (L.2). 



Fig. 65. — Through the mouth (w.) and the pharyngeal diverticulum {div.). The left half [op.) of the 

 operculum is directed straight forwards [i. e., away from the stalk), while the right half is folded 

 backwards in a complicated manner, and thus does not appear in the section. The right arms, 

 which are beginning to appear, are with the exception of R. i all thrown back along the posterior 

 side of the metasome, while the left arms (seen in figs. 63, 64) are for the most part directed 

 forwards. The ventral side of the right arm-base {a. b.) shews no tracé of food-grooves. 



Fig. 66. — Through the mouth [in.) which opens into the recess [op. ree.) formed by the base of the 

 operculum. The part of the right lobe of the operculum marked op', is backwardly directed, 

 so that its oral surface faces posteriorly : ■ — the direction of this lobe is probably correlated with 

 that of the last arm, which is also thrown backwards; a.b., ventral surface of right arm-base. 

 The left collar-canal shews both its external [cc. e.) and internal [c.c.i.) apertures. The fold of the 

 body-wall between this and the left oviduct [ovd.) is of no special significance: — .r., problematical 

 tissue of right collar-pore; g.s., dorso-lateral grooves of pharynx leading from the dorsal diverti- 

 culum [div.) to the gill-slits. 



Fig. 67. — Through the ventral wall of the left collar-canal [c.c.) and through the external opening (e. f. ^.) 

 of the right collar-canal. The opercular recess [op. ree.) is still present. The fold of the body-wall 

 seen on the right side between it and the collar-canal appears from the reconstruction to be 

 correlated with the throwing back of the arms and of the operculum of this side. 



Fig. 68. — Through both gill-slits [g.s.) and the anterior horns of the metasomatic cavity [b.c.'^a.). The 

 collar-cavities [b.c."^) are here divided by a ventral mesentery [v.jiies.-). 



Fig. 69. — Through the region of the pleurochords (//.), on the aboral side of the gill-slits: — the muscles 

 seen in b.c.^a. in fig. 68 are continuous with those marked ins. in this figure. 



Fig. 70. — Immediately on the dorsal side of the dorsal lobe of the stomach : — ///. is probably the 

 posterior end of the pharynx (its passage into the oesophagus not being very obvious in sections 

 cut in this plane). 



Fig. 71. — Belonging to the individual shewn in figs. 60, 61, and cut in a frontal plane on the aboral 

 side of the origin of the stalk: • — /. ï'.' termination of the posterior vessel [p.v.) of the stalk on 

 the second stomach [stom.-). 



[Fig. •/ r ivas draivn wit/i Zeiss, DD Obj. — The other figiires were dramn zvitli Zeiss C, and none of 

 the draivings liave been rediiced]. 



