PLATE LXIL 



Explanation of the Letters. 



A. 



a', 

 ad, 



ae. 

 ai. 

 an. 

 B. 



b. 

 c. 



ceo. 



ch. 



ch'. 



ohn. 



cv. 



D,, D^. 



fg- 



G. 



9- 

 gv. 

 ib. 



Axial cord of the ray. 



Its branches in the dorsal skeleton. 



Its upward extensions into the plated perisome of 



the ventral side. 

 Ambulacral epithelium. 

 Primary interradial cords. 

 Anambulacral plate. 

 Basal. 



Radial blood-vessel. 

 The bands of more or less calcified connective tissue in 



the body-cavity. 

 Fibrillar sheath round the vascular axis of tlie stem. 

 Interradial portion of the circular commissure. 

 Cavities of the chambered organ. 

 Their downward prolongations into the stem. 

 The nodal enlargements of these peripheral vessels. 

 Cirrus-vessel. 



Second and fifth distichals. 

 Fore-gut. 

 Gut. 



Its epithelial lining. 

 Genital vessel, 

 lutervisceral blood-vessel. 



I. Basiradial ligament. 



Id. Dorsal ligament between the ray-joints. 



li. luterarticular ligament. 



Ip. Labial plexus. 



M. Mouth. 



in. Muscle. 



n. Ambulacral nerve. 



nr. Its oral ring. 



oh. Oral blood-vascular ring, 



ill, -^3- First and third radials. ■ 



Tc. Rectum. 



rp. Plug of calcareous tissue within tlie radial funnel. 



s. Spinelets on the anambulacral plates. 



stc. Subtentacular canal. 



svh. Subambulacral plate. 



sij. Syzygy. 



V. Central vascular axis of stem. 



jr. Kadial water-vessel. 



U'p. AVater-pore. 



wr. Water-vascular ring. 



lot. Water-tube. 



.r. riexiform gland. 



XV. Its ventral end which joins the labial plexus 



Explanation of the Colours. 



Black — The nervous system, both ambulacral and autambulacral. 



Green — The water-vascular system. 



Red — Tlie blood-vascular system and the plexiform gland. 



Diagrammatic longitudinal section of a Pentacrinus decorus. On the right side of the 

 figure the section cuts the anal tube, and on the left side it passes along a ray 

 and the base of an arm. 



