ON THE EXPERIMENTAL HYBRIDIZATION OF ECHINOIDS. 353 



DESCRIPTION OF PLATES. 



Lettering. 



a. cil. ep Anterior ciliated epaulette. 



al.a Antero-lateral arm. 



al.s Antero-lateral arm skeleton, 



an Anus. 



ap. r Apical end of body -rod. 



ech. r Echinus rudiment. 



gr. p Green pigment. 



g. s Gastrula skeleton. 



/. pcd Lateral pedicellaria, 



m Mouth. 



mesc Mesenchyme. 



p. cil. ep Posterior ciliated epaulette. 



p. ped Posterior pedicellaria. 



pd. a Postero-dorsal arm. 



pd. s Postero-dorsal arm skeleton. 



po. a Postoral arm. 



po. s Postoral arm skeleton. 



pro. a Preoral arm. 



pro. I Preoral lobe. 



pro. s Preoral arm skeleton. 



s Stomach. 



tu.f. Tube-foot. 



tu. f.l Primary unpaired tube-foot. 



tu.f. 2 Paired tube-foot. 



Description of Plates 19-25. 



Plate 19. 



Figs. 1-9. — E. esculentus% xE. esculentus $ . 



Fig. 1. — Gastrula. 65 hours. X 175. Commencement of skeleton. 



Fig. 2. — Prism larva. 3 days. X 100. From the ventral aspect. Commence- 

 ment of postoral arms. 



Fig. 3. — Pluteus. 4 days. X 100. From the dorsal aspect. Apical ends of body- 

 rods spinous. Commencement of antero-lateral arms. 



Fig. 4. — Pluteus. 10 days. X 55. From the ventral aspect. Commencement of 

 the postero-dorsal arms and of the skeleton of the preoral arms. 

 VOL. CCIY. — B, 2 Z 



