PLATE X. 



C. levinseni. 



Piers. Ill 125 are from a frontal scries of an adult zooid. The proboscis is in the normal position. 



Fig. III. — Through dorsal lobe of proboscis, which is here strongly infolded (cf. PI. Ill, fig. 24). 



Fig. 112. — Thirty four sections further. Through pericardium {per.), both proboscis-pores (/./.), and 

 anterior dorsal horns of the collar-cavities [h.cra.]. The oval line surrounding the figure indicates 

 the outline of the lumen of the coenoecial tube. 



Y\a, 113. Six sections further. Through the anterior end of the notochord [nch.), the lumen of which 



is here specially large. The ventral lobe of the proboscis (/>.) is about to separate from the 

 proboscis-stalk. 



pjCT. 114. Four sections further. The ventral lobe of the proboscis has just separated from the proboscis-stalk. 



Pio-. 115. — Seven sections further. Slightly dorsal to the mouth, through the transverse part of the 

 pigment-band {p.b.) of the proboscis: — prob.st., lobe of proboscis-stalk, cut .separately;/., fold 

 of ventral lobe of proboscis. 



Fi". 116. — Four sections further. Through the upper lip, which shews a distinct labial or oral groove 

 (/. '^) on each side of its median ridge. The ventral lobe (/.) of the proboscis is folded in a 

 complicated manner. The free edge of the left lobe {op. I.) of the operculum has appeared. 



Fig. 117. — Two sections further, still through the upper lip, with its oral grooves {l.g.). The course of 

 the food-groove of the fifth right arm {R. 5) round the ventral side of the arm-base is illustrated 

 by figs. 115 — 117, and shews the manner in which the grooves of the posteriorly directed arms 

 pass towards the mouth. 



Fig. 118. — Three sections further. Through the anterior wall {div.) of the pharyngeal diverticulum, and 

 the beginning of the metasome {met.): — b.m. ridge of basement-membrane in right collar-cavity, 

 indicating the base of the operculum. 



Fig. 119. — ■ Four sections further. Through the mouth {in.) and pharyngeal diverticulum {div.). The mouth 

 opens straight forwards, as in PI. IV, fig. 33. The left half of the operculum {op. I.) is folded, 

 and lies principally in the plane of the section. The right lobe {op.r.) has its free edge directed 

 towards the stalk, so that this lobe appears in the sections as far as fig. 123. The median part 

 of the operculum and the base of both of its lateral lobes is, however, turned away from the 

 stalk, so as to constitute the epidermic recess seen in figs. 121 — 123 (cf. I'l. 1\'. fig. 34): — 

 b.m., two ridges of basement-membrane indicating the base of the left lobe of the operculum. 



l-'i'T. 120. — Two sections further. The dorsal wall of the pharynx is beginning to be distinctly trilobed. 

 This condition, which is more marked in fig. 121, indicates the commencement of the dorso- 

 lateral grooves {g.s.) which lead to the gill-slits and pleurochordal grooves. The emargination in 

 the dorsal body-wall of the metasome is a short longitudinal groove between the regions of the 

 two oviducts, and may have something to do with directing the faeces when they escape from 

 the anus. 



Pi,T. 121. Two sections further. Part of the thin dorsal wall of the right collar canal is cut: or.s. is 



possibly a vascular sinus. 



Pi<r. 122. — Three sections further. The mouth (w.) opens into the epidermic recess {op.rec.) constituted 

 by the base of the operculum. The median dorsal groove of the pharynx seen in the previous 

 sections has died away. 

 Fig. 123. — Six sections further; through the ventral end of the mouth and both gill-slits. The rectum (;-.) 



has appeared. 

 Fi<'. 124. — Five sections further. The distinction between the ordinary pharyngeal epithelium and the 

 pleurochordal tissue is much less marked than in C. dodecalophus. The anterior horns of the third 

 body-cavity are opening into the main cavity, of which a lobe divided by the ventral mesentery 

 {v.ines.'^) appears between the pharynx and the collar-cavity: — g.s., basement-membrane of 

 ventral (posterior) wall of right gill-slit; ov.v., ventral edge of ovarian vessel. 

 Y\". 125. — Thirteen sections further. The pleurochordal tissue has almost disappeared. The nerve-layer 

 has become very indistinct, and is not represented. 



[ The figures zoere all draion zi'llh ZEISS, C Obj., and reduced -\^. 



