16 ERNEST WARREN. 



EXPLANATION OF PLATES I AND II, 



Illustrating Dr. Ernest Warren's paper, " On the Anatomy of 

 a New South African Hydroid, Bimei'ia rigid a sjp. n." 



Fig. 1. — X 180. Vertical, longitudinal section of young liydranth 

 before the tentacles have appeared ; covered with a thin, continuous 

 layer of perisarc. 



Fig. 2. — X 180. Vertical, longitudinal section of young hydranth 

 with tentacles in process of growth ; mouth has not yet been formed ; 

 covered with a thin, continuous layer of perisarc. In the middle of the 

 hypostome region the ectoderm has thickened, and a split (e. c.) has 

 appeared in it ; this is the beginning of the ectoderm cavity which is 

 formed above the mouth. 



Fig. 3. — X 180. Vertical, longitudinal section of an adult hydranth, 

 showing soft perisarc (s.^ir.) over the hypostome region and extending 

 over the upper surface of the tentacle, ectoderm chamber (e. c), glandular 

 oral endoderm (g.o.e.), two of the four endoderm projections {e.pr.), 

 empty calyx-cavity (e. cy.) and nematocysts (n.). 



Fig. 4. — x 180. Transvei'se section near apex of hypostome of adult 

 hydranth, showing soft perisarc and opening of ectoderm chamber (o. e. c.) 

 to the exterior. 



Fig. 5. — x 180. Transverse section of hypostome region at the level 

 of the mouth, showing ectoderm chamber (e. c.) and mouth (;».). 



Fig. 6. — X 180. Transverse section of hypostome region at some 

 little distance below the mouth, showing the four endoderm projec- 

 tions {e.pr.). 



Fig. 7. — X 180. Transverse section through calyx region, showing 

 empty cavity (e. cy.), calyx-wall with perisarc ridges of older tentacles 

 (r. (1. t.) and of younger tentacles {r.y. t.), and the lower portion of the 

 body of the hydranth with coelenteron (Cce.). 



Fig. 8. — X 180. Transverse section through the hydrocaulus just 

 below the hydranth, showing the solid endoderm (en.) with coelenteron 

 entirely occluded. 



Fig. 9. — x 180. Vertical, longitudinal section of expanded adult 

 hydranth in feeding attitude, showing endoderm projections (e.jjr.), the 

 glandular oral endoderm (g. o. e.) exposed to the water, the ectoderm 

 chamber {e. c.) thrust to the edge, and the muscular ectoderm (hi. e. t.) 

 of the tentacle. 



Fig. 10. — X 300. Horizontal section of an endoderm projection close 



