PLATK III. 



Figs. 22, 25 — 32. — C. gracilis. Fig?. 23, 24. — C. levinseni. 



Fig. 22. C. gracilis. — View of a reconstruction, made by the ground glass method, with the assistance of 

 a plasticine reconstruction, from the specimen shewn in PI. V, figs. 43 — 53. The details of the first 

 arm (A'./) are based on the individual shewn in PI. I, fig. 7. The lateral flexure of the specimen 

 indicated by figs. 45 — 53 has for the most part been omitted. The left ovary [ov.l.) is mainly 

 occupied by a single large ovum. The broad pharynx {ph.) is seen from its narrow edge, the sharp 

 bend just before its junction with the oesophagus [oes.) being probably the result of muscular 

 contraction, which has also affected the dorsal vessel [d.v.]. The last four arms [R.2 — j) have been 

 cut off near their bases, which in tiie case of R.j — 5 pass transversely outwards, while R. ^ is 

 rotated round its own longitudinal axis so much that its groove faces posteriorly. 



Fig. 23. C. levinseni. — A reconstruction similarly matlc by the ground glass method; seen from the 

 posterior surface and somewhat from the left. The proboscis (p.) is directed forwards, shewing the 

 long, narrow proboscis-stalk {prob.st.) characteristic of this species; its morphologically anterior 

 epithelium is infolded in a complex manner. There is also some rotation of the proboscis-stalk 

 round its principal axis, since the left proboscis-pore [p. p. I.) lies at the edge of the drawing, while 

 the right pore [p.p.r.) is also brought to the left of the median plane of the metasome. The right 

 arms are already separate from one another, but R.2 turns ventrally from its origin, and is not 

 visible in this view. On the left side, the section passes at a more ventral level, so that the common 

 arm-base {a.b.) is seen, continuous with the left lobe of the operculum [op.]. The region of the 

 central nervous system [c. n. s.) is conve.x, and through it is seen the notochord (nch.). The dorsal 

 vessel (d. v.) lies in the dorsal mesentery ((/. ;«.), and the left ovarian vessel {ov. v.) is also seen : — 

 r. is a lobe of the rectum; g. s., seen tlirough the left ovary, is the projecting portion of the 

 pharyngeal wall leading from its dorsal diverticulum to the external aperture (g. s. e.) of the slit. 



Fig. 24. C. levinseni. — Anterior view, seen somewhat from the right side, of the same reconstruction, the 

 details of the upper lip added from a plasticine reconstruction. The arms are omitted, with the 

 exception of part of R.2. In addition to the median ventral projection of the proboscis-stalk, the 

 upper lip is traversed by two ridges on each side, thus giving rise to three oral grooves on each 

 side of the middle line. The greater part of the ventral wall of the mouth is cut away, with the 

 exception of a fragment of the lower lip, seen in the foreground, in the middle line. The convex 

 dorsal wall of the pharynx (ph.) is exposed, on either side of which is one of the deep pleurochordal 

 grooves; the right gill-slit [g.s.), cut near its external aperture, opens nearly vertically into one of 

 these, and on its median side is seen the blind end of one of the anterior horns of the metasomatic 

 cavity (b.c.'^a.). The right collar-canal has its external opening {c.c.e.) directed dorsally, while 

 between this and the internal opening is the problematical tissue {x.) of the collar-canal, attached 

 above to a fold of the body-wall of the collar. The free edge of the right lobe of the operculum 

 {op.) is directed dorsally, that of the left lobe ventrally. 



Fig. 25. C. gracilis. — Another view of the specimen shewn in fig. 22, from a plasticine reconstruction. 

 The thickness of the layers of plasticine having been somewhat too great, the transverse diameter 

 is exaggerated. The figure shews that both the operculum and the arms are modifications of the 

 anterior free edge of the collar: — g-s.r. right gill-slit; c.c.e. external opening of right collar- 

 canal; g.s. I. position of opening of left gill-sIit; b.iv., body-wall of metasome. 



Fig. 26. C. gracilis. — - Base of stalk of fig. 7 (Zeiss, DD): d., basal disc; /., proboscis of bud. 



Fig. 27. C. gracilis. — Base of stalk of a functional zooid, with a young bud (Zeiss, C). The collar of the 

 the bud shews indications of the first pair of arms [a.); and both the first {l>.c.^) and second (b.c.-) 

 body-cavities are visible. 



Fig. 28. C. gracilis. — Part of stalk of Fig. 29, shewing the two stalk-vessels (ZEISS, C). 



Fig. 29. C. gracilis. — Posterior view of metasome of a bud, at about the stage of fig. 32, shewing the 

 posterior vessel ip-i'.) of the stalk ending on the alimentary canal, and the anterior vessel (a. v.) 

 prolonged for a short distance along the anterior body-wall (Zeiss, C). 



Fig. 30. C. gracilis. • — Anterior view of a bud (Zeiss, C). The left half of the proboscis is injured, and 

 the first arm of the same side has been lost. The mouth (w.) is seen through the proboscis; the 

 arms possess terminal vesicles, and the bases of the posterior pair are continuous with the oper- 

 culum (op.), the free edge of which is indicated by a circular line partly surrounding the mouth: — 

 al., developing alimentary canal. 



Fig. 31. C. gracilis. — Advanced bud, seen from the left side (ZEISS, C), shewing the course of the food- 

 grooves of the first three left arms {L. / — .?): — /., edge of proboscis, which covers the greater part 

 of the bud; >//., mouth, seen through the proboscis; op. I., left lobe of operculum; c.c.e., external 

 aperture of left collar-canal; g.s.e., e.xternal aperture of gill-slit; ph., pharynx -j- oesophagus; 

 int., intestinal limb of alimentary canal. 



Fig. 32. C gracilis. — Posterior view of a similar bud (Zeiss, C): c. n. s., position of central nervous 

 system; R.i, first right arm, thrown over to the leftside; and, like /,..> and Z..J, possessing terminal 

 vesicles; m., mouth, seen through the rectum and pharynx. 



[figs. 22 — 2j -tvere drawn by 'Sir V.. WiLSON. All the figures zvere reduced -/j]. 



