PLATE VIL 



C. sibogae. 



Figs. 72 — -jè, jCj. ■ — Male. 

 Figs. J-J, 78. — Neuter. 



Fig. 72. — YoLing male, posterior view. The left arm has been broken off, but its base is indicated by 

 L. a. The refractive vesicles of which the epidermis of the arms of the male is almost entirely 

 composed are not indicated in figs. 72 — jt, but they have the character shewn in PI. IX, fig. 99: — 

 c.n.s., position of central nervous system. 



Fig. 72- — Older male, shewing the right testis {t. r.). The left testis is smaller and is seen through the 

 right arm [R. a.). The left arm [L. a.) is bifurcated at the tip. The arms are shorter than usual. 

 The proboscis (/.) is a good deal folded. 



Fig. 74. — Male, intermediate in age between figs. 72 and J2i- The collar [c.) is marked off from the 

 metasome (met.) by a conspicuous dorsal groove. The left side of the proboscis (p.) is somewhat 

 injured. Both arms are incomplete distally. 



Fig- 75- — Old male, seen obliquely from the right side. This specimen was cut into the sections represented 

 in PI. VIII, figs. 80 — 89. The right and left testes (t.r.,t.l.) are fully developed, and the metasome 

 [inct.) forms much the largest part of the animal. The arms [R.a., L.a.) are shorter and thicker 

 than in most of the young individuals. 



Fig. y6. — Anterior view of old male, with longer arms. Some of the details of this specimen are further 

 illustrated in PI. IX, figs. 95, 96. 



Figs. jj, 78. — Transverse sections of a neuter. 



Fig- 77- — Through both apertures of the right collar-canal, and the external aperture (g.s.e.) of the right 

 gill-slit. The muscular system is unusually strong in the neuters of C. sibogae: — ins. muscles of 

 metasome, passing to septum ^/^ [s.-j^]; from the anterior side of this septum originate the oral 

 muscles (or. /«.), some of the fibres of which spread over the dorsal side of the mouth. The three 

 epithelial ridges seen on the dorsal side of the pharynx pass in the section next in front of this 

 one into a triangular upper lip which is of the same size as the three ridges together. The two 

 groeves marked ///. pass laterally to the exterior, two sections on the ventral side of fig. jj; the 

 mouth being thus situated at the level marked iii. The operculum [op.) is directed forwards on 

 the right side, and backwards on the left side. 



Fig. 78. — A more posterior section of the same specimen. The gill-slit [g.s.) on the left side shews both 

 its internal and external apertures. That on the right side is cut on the posterior or dorsal side 

 of its external aperture ; in the next section further back the deeply stained epithelial lobe between 

 the two arrows has disappeared, and the vacuolated tissue of the gill-slit has become continuous 

 with the extensively developed pleurochordal tissue of the dorso-lateral part of the pharyn.x. The 

 whole of the arms of the right side are indicated (A'. / — ^). 



Fig- 79- — Obliquely sagittal section of an old male. The space between the central nervous system (r. «.j.) 

 and its basement-membrane is probably an artefact. The collar is cut in a plane which is inter- 

 mediate between sagittal and frontal : thus the projection L.a. is the base of the left arm, between 

 which and the posterior wall of the proboscis is a groove (f. cl.) corresponding with the principal 

 food-channel of an ordinary Cephalodiscus; f.c.r. is the corresponding groove of the right side, 

 and both grooves unite in the mouth, which occurs in a later section : — R. a. appears to be 

 part of the right arm; while the arm cut transversely seems to be that of the left side; — c.c, 

 right collar-canal; t.r.,t.l., right and left testes. The section does not involve more than half 

 the length of the animal, which is bent into a f^-form, in accordance with the shape of the 

 coenoecial cavity in which it lies. The metasome and the testes are thus at least twice as long 

 as the parts shewn. 



\Figs. ■J3 — jó ivere drawn zvith Zeiss A Obj.; -j-j — ■]g witli C Obj. None of //ie draiuings have been rediieed]. 



