A MONOGRAPH OF THE EXISTING CRINOIDS 61 



The ciliary epithelium, characteristic of the ambiilacral groove, begins at the base 

 of every group of tentacles. The ambulacral furrow itself is slightly concave and 

 ciliates strongly toward the mouth. The mucus is secreted in the ambulacral groove 

 by the mucus glands, and by it the grains are fastened together into larger lumps, 

 which are transported to the mouth, the edges of which are often pressed together 

 like a pair of lips during movements similar to swallowing. The centripetal ciliary 

 currents were also observed in Hathrometra and in Rhizocrinus. 



In a healthy animal that does not receive any great amount of nourishment at 

 one time the mouth is shaped like a slit. This slit in Antedon petasus is always 

 oriented from the anterior radius toward the posterior interradius, or in the anterior 

 half twisted a little to the left of the same line. Gislen observed a slit-shaped mouth 

 with the same orientation in a specimen of Thaumatometra comaster preserved in spirit. 

 In Heliometra glacialis the slit has the same orientation as in Antedon petasus but is 

 directed a little more obliquely, from the right anterior interradius toward the left 

 posterior radius, and the same condition is found in specimens of Poliometra prolixa, 

 Asterometra anthus, and Oligometrides adeonae. The mouth is twisted still more in 

 the same direction in Tropiometra ajra macrodiscus, in which it looks as though it 

 might become almost transverse in position, as in the Comasteridae. Most of the 

 crinoids preserved in alcohol that Gislen examined have a rounded mouth opening, 

 like sickly or dying individuals of Antedon petasus. 



All kinds of small particles eddying up from the bottom owing to the movements 

 of the animal or by currents in the water — mostly the latter — are carried to the mouth; 

 in other words detritus and benthonic organisms, as well as some part of the plankton 

 that rains down. Gislen's experience seemed to show that the benthonic nourishment 

 is the most important. The following are analyses of samples of excrement from 

 living animals examined: 



Antedon petasus. — All the samples were brought home from Smedjan, Kristine- 

 berg, Sweden, where the animals were dredged from a depth of 30-40 meters. 



1. A rough sample. The recently dredged animals were put into a vessel of sea 

 water where they were allowed to stay for some hours, and the abundant excrement 

 evacuated was collected. This contained detritus, small grains of sand, threads of 

 algae, diatoms, some peridineans, crustacean larvae (0.3-0.5 mm. long), small cope- 

 pods (0.09 by 0.18 mm.), macerated pieces of plants (one piece 0.40 by 0.60 mm.), 

 and a half-digested myzostomid. 



2. A lump of excrement taken directly from the anal opening contained detritus, 

 diatoms (Coscinodiscus, Navicula, Nitschia, etc.), copepods, an ostracod, a veliger 

 larva, a Ceratium, and a few living infusoria. 



3. Some food sucked from the mouth by means of a pipette included detritus, 

 diatoms, copepods (empty casings), some ostracods, one veliger larva, nauplius larvae, 

 empty podiae of small crustaceans, a peridinean, and a few sponge spicules. 



The following are analyses of samples of excrement from preserved specimens: 

 Meiacrinus rotundus, Sagami Bay, Japan, 180 meters. The excrement was 

 collected from the bottom of the vessel in which the animal had been laid. It con- 

 sisted of detritus, diatoms, tissues of more highly organized plants, solitary crusta- 

 cean podiae, crustaceans, and Foraminifera. 



