PLATE XXIII. 



SIDEKAKTK.EA SIDEREA (Ellis & Solander). 



Fig. 153. — Transverse section through the stomodseal region of an adult polyp. Six pairs of complete mesenteries 

 constitute the first, cycle, six alternating pairs the second cycle, and only ten pairs are present in the third 

 cycle. At this level the mesenteries nowhere extend as far as the peripheral limits of the intersepta] 

 loculi. Both mesenteries and loculi are interrupted by the synapticula which connect adjacent septa. 

 Septa occiii- within both the entocceles and exocceles, and in some cases are fused at their central termi- 

 nation. X 100. 



Fni. 154. — Transverse section through the upper part of the disk of a retracted polyp. The discal walls are resting 

 direetlyupon the tissues covering the septal edges. The simple apical knobs of two exocoelic tentacles 

 (represented diagrammatically ) are seen lying directly over the edge of the exosepta. < 111). 



Fio. 155. — Transverse section through the lower pari of the disk of the same retracted polyp. The section at this level 

 includes the synapticula, which are seen perforating the mesenteries, and an entoccelic tentacle with two 

 apical knobs, one on each side of the entosontuiu. X HO. 



Fig. 156. — Tangential section through a part of the peripheral region of a polyp, exhibiting the short vertical extent 

 of the mesenteries, and also the slight increase in thickness of the skeletotrophic tissue from above down- 

 ward. The column wall rests directly upon the tissues covering the septa, and is thrown into ridges and 

 grooves corresponding with the septa and mesenteries. X 70. 

 ti-l-t 



