PLATE XXII. 



M.KAXDRIXA LABYRINTHICA (Ellis & Solander). 



Fig. 147. — Transverse section through two stomodseal ridges opposite the insertion of the mesenteries, Bhowing the 

 difference in histological character between the ectoder f the ridges and that of the grooves, X 300. 



COLPOPHYLLIA GYROSA (Ellis & Solander). 



Fig. 148. — Section through the convolutions at the free extremity of a single mesentery; each convolution is termi- 

 nated by a mesenterial filament. X 70. 



OCULINA DIFFUSA Lamarck. 



Fig. 149. — Portion of a branch of a living colony, showing the different forms assumed by tlie polyps on expansion 

 and retraction. 



SIDERASTR.EA SIDEREA (Ellis & Solander). 



Fig. 150. — Retracted polyp. The septa are seen through the partly transparent polypal wall?, and superficially the 

 arrangement of the entocoelic and exoccelic tentacles on the disk. The Roman numerals indicate the 

 cycles to which the entotentacles and entosepta belong, the outermost cycle comprising only exotentacles 

 and exosepta. The first, second, and third cycles of entotentacles and entosepta are complete, except 

 that a third-cycle tentacle and septum are wanting in the lower left-hand system. In the upper left- 

 hand system a fourth-cycle entotentacle and entoseptum have appeared. 



Fig. 151. — Fully expanded tentacles: a, Bifurcated entocoelic; b, simple exoccelic. Enlarged. 



Fig. Iol'. — An interseptal lamella from & radians, freed by decalcification and slightly magnified. When in situ the 

 lamella lines the two walls of an interseptal loetilus and incloses a mesentery; the left vertical border is 

 peripheral, the right central; the curved upper border is in continuity with the disk, the lower is 

 adjacent to a dissepiment. The three vertical rows of apertures represent the spaces formerly occupied 

 by synapticula. ■ 20. 

 (54L> 



