108 



Fig. W. The aboral terminal surface of an arm-vertebra: a, ambulacral plates; 

 h, adambulacral plates; n, the furrow for the ambulacral vessel. 



Fig. 20. The oral terminal surface of the first free arm-vertebra: c, dorsal mar- 

 ginal plates; a, h, n, as in the preceding figure. 



Fig. 21. The extremity of the skeleton of the arm, strongly magnified, viewed from 

 above: a, the terminal spine-covered calcareous plate. 



Fig. 22. The same viewed from below. 



Fig. 23. A complete pedicellary from the cuticular sheath of one of the oral spines, 

 strongly magnified, viewed from the broader side. The exterior cuticular sheath has been, 

 by means of a solution of potash, rendered transparent; so that the enclosed calcareous 

 particles appear distinctly. 



Fig. 24. The same, viewed from the narrower side. 



Fig. 25. The calcareous skeleton of the same pedicellary, still more strongly magni- 

 fied, viewed from the broader side: ah, the side pieces (a, the proper forceps or jaw; 

 }), the lower perforated plate for insertion of the adductor-muscles); c, the middle piece 

 (the articulation-plate). 



Fig. 26. The same viewed from the narrower side: m m, the adductor-muscles; 

 a, h, c, as in the preceding figure. 



Fig. 27. The skeleton of a pedicellary from the cuticular sheath of one of the arm- 

 spines, viewed from the broader side, with closed jaws. 



Fig. 28. Another with widely opened jaws. 



Fig. 29. The same viewed from above: for all 3 figures the indication a,b,c, as in 

 figures 25 and 26. 



Fig. 30. The extremities of the closed jaws, viewed from above, to shew their 

 toothed edges. 



Fig. 31. Some of the developing cells of the pedicellaries from the base of the 

 cuticular sheath of an arm-spine. 



Fig. 32-37. Pedicellary-cellsin 6 diiferent stages of development, strongly magnified. 



Fig. 38. A litle young Brisinga coronata, viewed from above, natural size. 



Fig. 39. The same magnified, viewed from above. 



Fig. 40. A part of the same, still more strongly magnified, viewed from below: 

 ad\ the 2 adambulacral plates meeting in the angle of the arms; m, the oral membrane; 

 0, the oral aperture. 



Fig. 41. Skeleton of a pedicellary from the cuticular sheath of one of the oral 

 spines in the Brisinga endecacnemos, for comparison with fig. 25. 



Fig. 42. Skeleton of one of the larger sort of pedicellaries from the cuticular 

 sheath of one of the arm-spines of the same species, for comparison with fig. 27. 



