EXPLANATION OF THE PLATES. 



The following letters are em|iloyeil throughout all the Plates :- 



A. 

 a. 

 a. 

 at: 



ad. 



ae. 



ai. 



an. 



ar. 



at. 



B. 



B„B. 



h. 



hr. 



a 



c. 



ca. 



cc. 



ceo. 



ch. 

 cli. 



chc. 



da I. 



Axial cord of the ray or arm. 



Axial cord of a pinnule. 



Branches of the axial cord in the skeleton. 



Connective - tissue fibres between the 



auauibulacral plates. 

 The parambulacral extensions of the axial 



conls into the ventral perisome. 

 Ambulacral epithelium. 

 Primary interradial cords. 

 Anambulacral plates. 

 The secondary (radial) cords. 

 Anal tube. 

 Basal ring. 



First and second brachials. 

 Eadial blood-vessel. 

 Ligaments uniting the basals to the top 



stem-joint. 

 Plug of calcareous tissue in the radial 



funnel, called a rosette by Sars. 

 The body-cavity or coelom. 

 Tlie bands of connective-tissue which 



traverse it. 

 Fibrillar sheath round the vascular axis 



of the stem. 

 Its radiating extensions. 

 Coeliac canal. 



Interradial portion of the circular com- 

 missure. 

 Cavities of tlie chambered organ. 

 Their downward prolongations iuto the 



stem. 

 . Fibres of connective tissue whicli traverse 



the fibrillar envelope of the chambered 



organ (central capsule). 

 . Tlie nodal enlargements of the peripheral 



vessels of the stem {ch'). 



(ZOOI- CHALL. EXP. PART XXXH. — 1884.) 



