PLATE XXIV. 



SIDERASTR/EA SIDEREA (Ellis and Solander). 



F „. 157 _p„ r tion of the skeletotrophic wall with a mesentery attached, from the middle region of a polyp. The 

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

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



Fir 158 -Transverse section through an incomplete mesentery in the stomodaeal region. The incipient mesenterial 

 filament the mesogloeal plaitings supporting the retractor muscle, and the glandular character ot the 

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

 resorption toward its axed extremity, and is free from the skeletotrophic tissues and greatly narrowed. 



X 300. , , . , - f i •. 



Fig 159.-Transverse section through a mesentery, a short distance below the stomodaeal 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 ot the 

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

 of the mesentery to the septal invagination. X 300. 



Fig I60.-Portion of the skeletotrophic wall from the lower region of the polyp. It differs but little from its char- 

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



AGARICIA FRAGILIS Dana. 



Fig 161 -Transverse section through a polyp immediately below the stomodseal region. No regular alternation of 

 larger and smaller mesenterial pairs can be established, and no directives occur. At the upper right- 

 hand corner two mesenteries are united by their free extremity. X 70. 



Em 169 -Transverse section through the upper part of a portion of two retracted polyps. Thepolypal walls all 

 round are practically resting upon the septo-coste. In the middle left of the section the exsert septo- 

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

 are continuous. Tin- gastro-ccelomic cavity of the two polyps are likewise in communication along 

 the sides of the septo-costse. < >n the upper right the mesenterial chambers and mesenteries have been 

 broken up by the formation of synapticula. • .0. 



Fig. 163.— Radial section of a portion of the disk showing a slight tentacular prominence. X 110. 



646 



