PLATE XIV. 



EMBRYOS. 



Figs. i86 — 197. — C. gracilis. 

 Figs. 198 — 210. — C. levinseni. 



Fig. 18Ó. C. gracilis. — Two cell stage, mounted whole. 



Fig. 187. — Ventral view of an ad vaneed embryo. 



Fig. 188. — Lateral view of a similar embryo: — b.cr, position of collar-cavity. 



Fig. 189. — Optical frontal section of a similar embryo from the ventral side. The constrictions at the 



sides of the yolk [yk) correspond with those in which the collar-cavities lie in other preparations; 



V. inv., external aperture of the ventral invagination. 

 Fig. 190. — Actual frontal section, more highly magnified : — v.inv., dorsal wall of ventral invagination, 



cut tangentially (other sections of the same embryo are shewn in figs. 195, 196). 

 Fig. 191 — 194. — Transverse sections of a similar embryo. Fig. 191 is through the anterior sense-organ 



(.f. ö.); fig. 192, through the anterior part of the ventral invagination (v.inv.); fig. 193, through 



the collar-cavities [b.c.-] and the metasomatic cavities (b.c.^'); and fig. 194, through the metaso- 



matic cavities (b.c.^'). 

 Figs. 195, 196. — Horizontal sections of the individual shewn in fig. 190. 

 Fig. 195 is through the dorsal region of the embryo; — b.c.'^, collar-cavity. 



Fig. 196 is between fig. 195 and fig. 19O: — vac, vacuolated ectoderm, extending as far as the two arrows. 

 Fig. 197. — Nearly median sagittal section of a similar embryo. The region of the posterior pit [post.p. 



is, however, cut somewhat frontally, so that both third body-cavities {b.c?) are visible. The 



somewhat crumpled vitelline membrane (v.m.) is seen, while between it and the ectoderm are 



what are probably excretory granules [exc). The anterior ectoderm between the two arrows has 



the vacuolated character shewn in fig. 190. 

 Figs. 198 — 210. C. levinseni. 

 Fig. 198. — Advanced embryo, seen obliquely from the dorsal side. The central yolk-mass [yk] has a 



lumen; the edge of the reflected part of the yolk is not easily seen where it crosses the central 



mass, but is probably correctly represented: ■ — vac, vacuolated ectoderm, which in the embryos 



of this species contains numerous refractive bodies. 

 Fig. 199. — Another embryo, probably somewhat older than fig. 198, seen from the side. The embryo was 



found in a peristome, close to its orifice, and may have been about to be liberated. 

 Fig. 200. — Advanced embryo of unusual appearance, in which the vacuolated ectoderm [vac.) and the 



ventral thickening (i<. f.) have together the appearance of the proboscis of the adult. 

 Fig. 201. — Obliquely sagittal section of an advanced embryo. The vacuolated ectoderm (ï'rtc.) is invaginated 



dorsally and in front. It is uncertain whether the collar-cavity is seen on the ventral side, which 



is turned to the right. A space (artificial r), which is also seen in fig. 202, occurs outside the 



basement-membrane (b. m.) at the anterior end. 

 Figs. 202 — 206. — Five sections of a transverse series of a similar embryo. The limits between the second 



and third body-cavities are not obvious in this series. 

 Fig. 202. — Through the anterior end. 

 Fig. 203. — Through the anterior yolk-mass. 



Fig. 204. — Through the central yolk-mass, which is here encircled by the reflected part of the anterior yolk. 

 Fig. 205. — Through the extreme posterior end of the ventral thickening. 

 Fig. 206. — Through the extreme posterior end of the anterior yolk-mass. 

 Fig. 207 — 210. — Four sections of a frontal series of an older embryo. 

 Fig. 207. — Through the entire area of the ventral thickening [v.t.]. 

 Fig. 208. — Near the ventral surface, but cutting the five coelomic spaces. 

 Fig. 209. — Through about the middle of the embryo. 

 Fig. 210. — Through the dorsal half of the embryo. 



\Figs. igo — /p7 were drawn zvith Zeiss, D D ObJ.; figs. 1S6 — iS^ and ipS — 3zo with Zeiss, C. AU the 

 figures zuere rediiccd ^/j]. 



