MONOGRAPH OF THE EXISTING CRINOIDS. 315 



In Neocomatella pulchella the form of this epithelium is more easily seen. The 

 cells, the borders of which can rarely be determined, are approximately cubical, and 

 their position is indicated by their dark-colored nuclei. 



In Antedon mediterranea, Tropiometra carinata, and Neocomatella pulchella 

 apparently in all comatulids the connective tissue layer is divisible into two strata, 

 of which the more superficial is composed of a loose union of fibers running in 

 every direction, while the deeper, bordering the ccelomic epithelium, shows a 

 cartilaginous consistency. In this connective tissue layer are nerve branches, which 

 run parallel with the surface, from which nervules proceed to the epithelium. It 

 is traversed by the water pores, which lead into the body cavity. 



The ambulacral grooves lead from the pinnules to the arms, down the center 

 of the ventral surface of each arm, and across the disk, converging at the mouth, 

 about which they unite to form a ring-like area. They are bordered on either side 

 by lappets and tentacles. 



The epithelium lining these grooves is greatly thickened. The constituent 

 supporting and sense cells, as well as the nerve fibrillar layer, have already been 

 described. 



Below this epithelium there is found in many species a schizoccele cavity, and 

 always a water vessel which leads out from a ring canal about the mouth. 



As the body cavity between the wall of the intestinal canal and the body wall is 

 traversed in all directions by connective tissue strands, it is often scarcely recog- 

 nizable as such, and in some places the distinction between the body wall and the 

 connective tissue strands can hardly be made out. But all the subdivisions into 

 which the body cavity is broken up are lined with enteroccele epithelium. 



BODY CAVITY. 



In the recent crinoids the development of mesenteries, bands, and septa travers- 

 ing the body cavity and serving to hold the internal organs in place has been carried 

 to such an extreme that the body cavity as a whole has vanished, and there is only 

 to be found a system of intercommunicating canals, which collectively are the 

 remnant of the original body cavity. 



In Isocrinus decants the body cavity within the calyx has entirely disappeared. 



In Neocomatella pulchella, as in all the large species of the Comasteridse, the 

 number of these bands and septa is very great, so that the body cavity is enormously 

 subdivided. These bands, of all sizes, form a maze of fibrous branches on all sides, 

 and are attached some to the intestinal wall, others to the body wall. 



Pigment and calcareous concretions occur in the bands, and in the species of 

 the genus Antedon, though rarely, sacculi. 



These bands are covered (that is to say, the remnants of the body cavity are 

 lined) with a very fine epithelium of flattened cells the oval nuclei of which stand 

 out prominently in the flattened cell body. Within the bands themselves are found 

 wandering cells lying in the gelatinous ground substance between spindle and star- 

 shaped cells. 



A cross section of an arm shows a continuation of the body cavity as at first 

 three canals, a dorsal and two ventral or subtentacular canals, which are separated 



