382 



after explained by other figures. By fig. 356 is represented the ordinary 

 appearance of the endorhin of silicified specimens when cleared of the 

 limestone matrix by treatment with acid. Although the pores have been 

 seen in this species only, yet it seems quite probable that they occur in 

 all others of the genus. 



In the diagram fig. 357 the tubes are placed proportionately much 

 farther apart than they are in any known species, in order to exhibit the 

 structure with the greater clearness. The endorhin is drawn as if it were 

 transparent to show the position of the tubes beneath it. The dotted lines 

 give the outhnes of the upper portions of the tubes, and also define the 

 course of the eudorhinal canals, — four radiating from the top of each tube. 

 The endorhinal pores — one situated at each of the points where the 

 angles of four plates meet — penetrate through the endorhin into the space 

 between the tubes, and not into the tubes themselves, as might be sup- 

 posed from a superficial examination. In the ectorhin the rough lines h 

 represent the sutures between the plates ; and it will be observed that 

 they have the same direction as the endorhinal sutures in the upper part 

 of the figure. The stolons have not the same direction as the endorhinal 



Fig. 357. 



Fig. 357. — Diagram to explain the structure of the body-wall of Rcccptaculilcs; b, the 

 endorhin ; c, the ectorhin ; d, suture between the plates of the endorhin ; 

 e, endorhinal pore ; /, endorhinal canal ; g, radial stolon ; A, cyclical 

 stolon ; /c, suture between the plates of the ectorhin. 



canals, but are, as it Avere, turned one-eighth round, so that the two direc- 

 tions are inclined to each other at an angle of 45°. The stolons run along 

 the inner surface of the ectorhin, but the endorhinal canals are excavated 

 in the substance of the endorhin. The space between the tubes is almost 



