552 DR J. STUART THOMSON ON 



trunk shows numerous small spicules, but in the central part they are fewer in number, 

 and of a different form. 



Spicules occur in the tentacles and crown, in the stomodaeal walls and around the 

 upper portion of the latter, in the calyx and in the trunk. These several parts are 

 marked either by different forms of spicules, or by spicules of different dimensions. 

 The crown and tentacles show long spindles, usually red in colour, yellow also occurring, 

 but not so abundantly. These spicules are, as previously stated, disposed en chevron, a 

 triangular stripe on each tentacle ; at the base of the tentacles, these spindles are 

 arranged so as to form a ring encircling the polyp. The spicules of the crown and 

 tentacles show the following dimensions: — 0'49 by - 05 mm. to 0*75 by 0*06 mm., 

 and 053 by 0*03 mm. to 0*56 by 007 mm. The spicules in the walls of the 

 stomodEeum (proper) are short, broad, spinous spindles, the latter have the following 

 dimensions: — 0"09 by 0'03 to 0'14 by 0"05 mm. The more external spicules 

 surrounding the stomodaeal part of the polyp are similar to those of the tentacles 

 and crown. 



The spicules from the external part of the calyx resemble in form those of the 

 stomodaeal wall (proper) ; the former are arranged en chevron in eight triangular stripes 

 or bands resembling so far the arrangement on the tentacles, but the stripes or bands 

 are connected with one another by a few intervening spicules. On retraction of the 

 polyp within the calyx, the distribution of the calyx spicules gives rise to a star-like 

 appearance. These spicules have the following dimensions : — 0"09 by 0*04 mm. to 0'14 

 by 0'06 mm. The spicules of the internal part of the calyx wall are, on the contrary, 

 long narrow spindles or rods resembling those of the tentacles, but their ontline is 

 slightly straighter, and they are colourless. Their dimensions are as follows : — 0"50 by 

 0-03 to 075 by 0'03 mm. 



The distribution of the spicules in the trunk is noteworthy. They are very 

 numerous in the external part of the coenenchyma or rind, but on the contrary only a 

 few occur in the central portion of the same, and are of a different form from those of 

 the exterior. The spicules of the rind are double spindles, and have the following 

 dimensions: — From O'll by 0'08 to 016 by 0'09 mm. 



The spicules of the central trunk are narrow, spinous spindles, and have the follow- 

 ing dimensions: — From 015 by 0'02 to 0'30 by 0'06 mm., and from 015 by 0"02 to 

 0-20 by 0-08 mm. 



The spicules of the colony may be briefly summarised as follows : — 



1. Long narrow spindles from the crown and tentacles of the polyp, frequently 



slightly curved ; colour, red and yellow. 



2. Short and broad, spinous spindles from the walls of the stomodamm (proper) and 



from the external part of the calyx wall ; colour, red. 



3. Long spindles or rods from the internal part of the calyx wall ; colourless. 



4. Double spindles from the external coenenchyma of the trunk. 



5. Spinous spindles from the central coenenchyma of the trunk. 



