320 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



to the base. The connective tissue layer, about 0.1 mm. thick, is composed of 

 spindle-shaped and star-shaiJed cells. In Antedon there is no calcification. The 

 muscular layer is develoiied in the form of a strong sphincter. 



The cords which establish the union between the gut and the body wall within 

 the anal tube are composed of connective tissue which outwardly passes into the 

 cutis and inwardly into the connective tissue layer lying in the gut wall just 

 beyond the ring muscle. 



Nerve branches proceed from the mesodermal oral nervous system and from 

 the lateral nerves of the water vessels and enter the connective tissue layer of the 

 anal tube, innervating partly the sldn and partly the musculature. 



Tlie histological structure of the gut is the same in all the comatulids in which 

 it has been studied. 



In the young of Antedon hifrda Sir Wyville Thomson described a " primitive 

 liver " which has not been mentioned by subsequent writers. 



Speaking of the adult A^itedori bifida, W. B. Carpenter states that in the 

 thickened disk which surrounds the mouth, formed at the junction of the perisome 

 of the oral disk with the wall of the alimentary canal, he detected a series of 

 csecal tubuli opening into the commencement or esophageal portion of the alimen- 

 tary canal. He suggests that these may have a salivary function. He also sug- 

 gests that the peculiar gland-like character of the plicated portion of the wall of 

 the inner side of the horizontal coil of the alimentary canal seems to render it 

 probable that it performs the function of a liver. 



Doctor Mortensen found that in Notocrinus viriJis the walls of the intestine 

 are greatly folded, a complete labyrinth of folds appearing on removal of the 

 slvin of the ventral side of the disk. The folds are not confined to the ventral side, 

 although most strongly developed there. A reticulate connective tissue, contain- 

 ing no calcareous deposits, fills the intei'stices between the folds. 



CHAMBERED ORG.^N. 



The chambered organ lies in the central cavity of the centrodorsal and is 

 completely incased by the nerve fibrillpe which collectively form the central organ 

 of the dorsal nervous system. 



Hamann, studying especially N eocomatelia pulchella., has worked out the struc- 

 ture of the chambered organ in great detail. He finds it to be the same in Neocovia- 

 tella pulchella, Comatula rotalaria, Comanthus parvieirra, Antedon mediten'anea, 

 and Heliometra glacialis. 



In the dorsoventral axis of the chambered organ there runs a cord which is 

 a dorsalward continuation of the axial organ lying within the calyx. This cord 

 is attached to the wall of the chambered organ by five radiating bands or septa, 

 which thus form five separate chambers. Ventrally, these five chambers contract 

 and run as narrow tubes close along the axial cord, soon ending blindly, and con- 

 necting bridges appear between the five radial mesenteries ; dorsally the chambers 

 are in commimication with the central vessels of the cirri into which derivatives 

 from the five septa run as flattened median partitions. The cirrus vessels are given 

 off only in the five meridians, though usually in several rows. Toward the center 



