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The stem is much more important than generally considered. It 
is composed of zodal and internodal joints, and continually increases 
in lengthin the growing crinoid by the production of new joints. 
The nodal plates in the Inadunata, Camerata, and a few of the Meso- 
zoic and recent crinoids, are introduced directly beneath the proximal 
plate of the calyx, so that the uppermost joint for the time being, is the 
youngest joint of thestem. In the young Comatula, however, in which 
the top joint subsequently develops into a controversal, in the Mesozoic 
Millerocrinus and Apiocrinus, in the recent Rhizocrinus and Calamo- 
crinus, and in all Ichthyocrinidae, forms in which the top joint in the 
early larva anchylose with the infrabasals, the new nodals are intro- 
duced below the top joint. The internodals are interposed between 
the nodal joints and increase continually in adownward direction dur- 
ing the life of the organisms pare passu with the formation of new 
nodal pieces. The stem matures from the root up, and remains per- 
manently in a state of immaturity at its upper end. The maximum 
number of internodal joints varies among different forms. Sometimes 
there are many to the internode, as in the case of most species of 
Platycrinus, in Mespilocrinus and Rhizocrinus : sometimes only avery 
few ; while Rhodocrinus, throughout its stem generally, has but one. 
The cirriin Paleozoic crinoids are, as a rule, more formidable than 
in later forms, and in most of them they are confined to the lower part 
of the stem, often occurring only at the distal end. They are given 
off from the nodal joints, and are generally arranged singly, rarely in 
whorls as in recent forms. 
It has been the general opinion that all Paleeocrinoids are fixed forms, 
but this view is not now believed to betrue. ‘The facts appear to lead to 
the conclusion that at least many of the species in the later part of life 
were free for a portion of the time, as in the case of the recent Penta- 
crinidze, in which the stem at some time at or nearthe maturity becomes 
separated fromthe root. The terminal end in most of the old crinoids 
tapers to a sharp point, but a root is rarely attached, while detached 
roots are found abundantly, but scarcely ever associated in the same 
stratum with the crown. 
The real morphological relations of the Basals and Infrabasals is of 
particular interest. The latter term is adopted for the first plates in 
the base, and ‘‘basals”’ for the circlet next to radials. The basals of 
dicyclic crinoids always consist of five pieces; the infrabasals of five, 
rarely three. In monocyclic forms the base is divided into five, four, 
