MONOGRAPH OF THE EXISTING CRINOIDS. 351 



In sagittal sections of the extension of the body cavity into the pinnules the 

 circular openings of these sacks are visible, surrounded by a swollen border. 

 Sometimes these openings are large, sometimes contracted; in the latter case the 

 organ has a spherical appearance. 



In Heliometra glacialis a structureless membrane separates the sacks from the 

 surrounding connective tissue. The epithelium lining the organ consists of high 

 cells which become flattened at the bottom of the sack and do not bear cilia. In 

 the upper part and about the opening the epithelium is greatly thickened, the cells 

 becoming more or less filiform with the oval nuclei, which lie in a swollen area, 

 sometimes nearer the base, sometimes nearer the summit. The long cilia are 

 attached to the cells by short foot pieces. 



In Comanthus parvicim*a Hamann found these organs mostly in the form of 

 closed sacks, 0.05 mm. long and 0.04 mm. broad. Their structure was essentially 

 the same as in Heliometra glacialis, but at the bottom there were lower cells and 

 on the sides and about the opening longer ciliated cells. 



In Isocrinus decants they also form closed sacks. 



In Antedon mediterranea they occur in large numbers. They have the same 

 structure as in Heliometra glacialis, but the ciliated cells run deeper into the cavity, 

 which beyond them is lined with cubical cells without cilia. 



These organs Hamann found to be best developed in Comatula Solaris. In 

 this species they lie closely massed in rows so that on a cross section through a 

 pinnule eight or more are cut through. 



The ciliated sacks serve to impart motion to the fluid of the body cavity. 



AMBULACKAL MUCUS CELLS. 



In 1902 K. C. Schneider first described in Antedon mucus-producing cells, 

 which he found scattered between the supporting and sense cells of the ambulacral 

 epithelium. 



These were subsequent!} 7 studied by Eeichensperger, who found them every- 

 where present in the ambulacral grooves of the disk, as well as in those of the arms 

 and pinnules, not only of Antedon mediterranea but of Isocrinus and of such of the 

 Comasteridse as he examined as well. 



Figs. 1317-1321, pi. 46. 



The sacculi are small, spherical bodies, easily visible under a hand lens, 

 ranged in an evenly spaced continuous row along either side of the ambulacral 

 grooves of the disk, arms, and pinnules. In the genus Antedon, and probably also 

 in other types, they occur in the walls of the digestive tube. P. H. Carpenter 

 found them in the lowest part of the cup of a larva with five cirrus stumps, just 

 above the chambered organ; but in other species he notes that they are either 

 entirely absent, or are invariably limited to the immediate neighborhood of the 

 water vessels. 



In life the sacculi are colorless, but in preserved specimens they are, as a rule, 

 conspicuous as blackish, dark red, greenish, purplish, or yellow dots. 



