PLATE XXIV. 



SIDERASTR.EA SIDEREA (Ellii- iiml SoUuuler). 



Fig. 1.57. — Portion of tlie .skeletotrophic wall with a mesentery attacheil, from the middle region of a polyp. The 

 mesoglcpa of the mesentery is greatly swollen and striated at the extremity where it comes in contact 

 with the skeleton, and the calicohlast layer, very broad elsewhere, is here absent. X 400. 



Fk;. 158. — Transverse section through an incomplete mesentery in the stomoda>al region. The incipient mesenterial 

 filament, the mesoglo'al plaitings supporting the retractor muscle, and the glandular character of the 

 mesenterial endoderni are represented. The peripheral end of the mesentery has already undergone 

 resorption toward its tixed extremity, -and is free from the skeletotrophic tissue.« and greatly narrowed. 

 X 300. 



Fic;. 159.— Transverse section through a mesentery, a short distance below the stomoda-al region, along with its 

 attachment to the skeletotrophic tissues. The mesenterial filament is here fully developed. The calico- 

 blast layer is as broad as the endodermal layer, and is highly granular and vacuolated; a portion of the 

 skeletal matrix is persistent on the right side. The mesogUca is expanded along the line of attachment 

 of the mesentery to the septal invagination. X 300. 



Fig. 160.— Portion of the skeletotrophic wall from the lower region of the polyp. It iliffers bat little from its char- 

 acter in the upper part of the polyp. X 400. 



AGARICIA FRA(;ILIS Dana. 



Piii. 161.— Transverse section through a polyp immediately below the stomodical region. Xo regular alternation of 

 larger an<l smaller mesenterial pairs can be established, and no directives occur. Xt the upper right- 

 hand corner tw(j mesenteries are united by their free extremity. X 70. 



Fig. 162.— Transverse section through the upper part of a portion of two retracted polyps. Thepolypal walls all 

 round are practically resting u])on the septo-costje. In the middle left of the section the exsert septo- 

 costa are seen in section free from the calicinal wall, and the mesenteries of the two adjacent polyps 

 are continuous. The gastro-ca-loinic cavity of the two polyps are likewise in communication along 

 the sides of the septo-cost». . On the upper right the mesenterial chambers and mesenteries have been 

 broken up l)y the formation of synapticula. X "0. 



p,,;. leii- Radial section of a portion of the disk showing a slight tentacular prominence. X UO. 



646 



