PLATE XXTT. 



M^ANDRINA LABYRINTHICA (Ellis & S.ilander). 



Fii;. U7. — Transverse section tlirough two stoniodfeal ridges opposite the insertion of the mesenteries, showing the 

 difference in histological character between tlie ectoderm of the ridges and that of the grooves. X 300. 



COLPOPHYLLIA (iYKOSA (Ellis & Solander). 



l'"iii. 14S. — Section through the convolutions at the free extremity of a single mesentery; each ciirivnhnion is termi- 

 nated by a nie.senterial iilament. < 70. 



OCULIXA DlFFrSA Lamarck. 



Fni. Hil. — Portion of a liranch of a living colony, showing tlic iliffercnt forms assumed liy the polyjis on expansion 

 and retraction. 



SIDEKASTK/E.\. SIDEREA (Ellis & 8olander). 



Fi(i. l.'iO. — Retracted polyp. The septa are seen through the ))artly transparent polypal walls, and superficially the 

 arrangement of the entoctelic and exoctelic tentacles on the disk. The Roman numerals indicate the 

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

 and exosejita. The first, second, ami 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 entoctelic; /(, simple exoccelic. Enlarged. 



Fig. 152. — Xn interseptal lamella from -S'. rddians, freed l)y decalcification and slightly magnified. When in situ the 

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

 peripheral, the right central; the curved upper border is in continuity w-ith the disk, the lower is 

 adjacent t(j a dissepiment. The three vertical rows of apertures represent the spaces formerly occupied 

 by synapticula. ?< 20. 

 642 



