45 



Fig. 43. Longitudinal section of ambulacial epithelium 



and tlie sub-epithelial nerve band, x 650. 

 Fig. 44. Portions of two transverse sections of the axial 



organ, x 320. 

 Fig. 45. Transverse sections of a group of tubular blood 



lacunae, x 180. 

 Fig. 46. Transverse section of the axial organ, x 180. 

 Fig. 47. Portion of a sagittal section of the disc, passing 



through the anal interradius. x 180. 



Plate V. 



Fig. 48. Side view of central capsule and pentagonal 



commissure of the apical nervous system, 



reconstructed from serial sections. x 20. 

 Fig. 49. Aboral view of central capsule and pentagonal 



commissure of the apical nervous system, 



reconstructed from serial sections, x 20. 



The cirrus cords are not represented in this 



figure. 

 Fig. 50. Sagittal section of an arm. x 40. The 



structures on the ventral side of the cceliac 



canal are not represented. 

 Fig. 51. The " spongy organ," as seen in a horizontal 



section of the disc, x 122. 

 Fig. 52. Diagram of a sagittal section of the disc, partly 



after Ludwig. 



Plate VI. 



Fig. 53. Horizontal section of a radial nerve cord at the 

 point of bifurcation to form the brachial cords, 

 showing the commissure and chiasma. x 55. 



Fig. 54. Horizontal section of the central capsule and 

 the chambered organ, at about the level of the 

 line * in fig. 59. x 40. 



