MONOGRAPH OF THE EXISTING CRINOIDS. 451 



The first three bands lie anterior to the internal organs over the region from 

 which later the stalk is formed. The third approximately indicates the dividing 

 line between the stem and calyx of the fixed larva. The fourth band surrounds 

 the posterior body region over the internal organs, and does not present any 

 marked irregularities. The fifth surrounds the posterior pole of the body beyond 

 the internal organs. 



In the ciliated regions the epithelium is thickened and arched outward, except 

 dorsally in the median line where it is more flattened; inwardly toward the body 

 cavity a feeble concavity may underlie the external more marked convexity. 



The cells are high prisms, pyramids, or spindles of extremely small diameter, 

 which extend from the exterior to the body cavity. On the outer side they bear 

 a glistening investment over a cuticle-like edging, striped at right angles to 

 the surface. 



The cilia are deeply inserted in the outer part of the cell body. The nuclei, 

 especially in hsematoxylin, stain very quickly and intensively. They are markedly 

 smaller than the nuclei of the cells in the intermediate zone and have greatly 

 increased in number by division during the preceding development period. Since 

 frequently a new nuclear division intervenes before the cell body has completed 

 a previous division, several nuclei can easily be found in a single cell. 



The nuclei of neighboring cells lie at different heights, but mostly near the 

 middle or in the inner cell half. 



Structurally closely related to the slightly protruding type of ciliated band 

 just described is another, which differs in that it does not rise above the general 

 body surface, but instead is somewhat depressed below it so that it forms a 

 shallow furrow. This occurs on the dorsal surface of the larvae in the median 

 line, and sometimes elsewhere. 



The glistening cells liere appear as extraordinarily attenuated pyramids, the 

 bases of which are toward the body cavity, while the cilia are attached to the 

 apices. Each cell apparently carries a single cilium. 



The four zones bounded by the ciliated bands and the posterior ring are 

 composed of considerably larger cells which lack the glistening character; in 

 end view these are irregidar polygons mostly six, sometimes five sided. The 

 nuclei are larger than those of the glistening cells, but much less easily stainable, 

 and lie mostly in the middle or near the inner end, very seldom toward the outer 

 end. In some no chromatin granules can be demonstrated, and it is possible the 

 chromatin may entirely disappear. Sometimes there are two nuclei in an 

 undivided cell body. 



Among the normally formed ectodermal cells there appear in later embryonal 

 life certain other elements. These may be described as club-shaped cells contain- 

 ing a nucleus and colored deep yellow ; the broader end is outward, and not only 

 reaches the surface but sometimes projects beyond it. 



After preservation in alcohol and staining in hematoxylin these structures 

 stand out intensively, and it is then easily seen that the coloration comes from 

 variously formed inclusions Ln the cells which lie at different heights, sometimes 



