40 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
crinus and Calamocrinus, and in all Ichthyocrinide, so far as observed, the 
new nodal joints were formed beneath the top joint, and the latter remained 
permanently attached to the calyx. In Apiserinus, in which for some dis- 
tance the upper end of the stem is greatly inflated, and the proximal joints 
extremely long, it is possible that the nodal joints were introduced below 
the inflated part, for there appear to be no immature segments between the 
upper joints. 
The internodal joints, as stated, are placed between the nodal ones ; and 
the spaces which they occupy, and which continually increased in length and 
width in the growing Crinoid, are the internodes. 
The increase in the length of the internodes took place gradually in a 
downward direction —as may be seen by comparing the stem of a young 
specimen with that of an older one — and pari passu with the formation of 
new joints just below the calyx. Hence in the upper part of the stem there 
is a variable number of premature internodes. Those nearest the calyx are 
the shortest, and consist of the smallest number of joints ; while the inter- 
nodes in the lower part of the stem all contain the same number of pieces, 
and all joints have approximately the same proportions. The joints of the 
upper part vary in the same internode from a growing leaflet, invisible in a 
side view, to an almost fully developed joint; and the upper internodes fre- 
quently consist of single pieces. But they are followed more or less rapidly 
by internodes of two, three, or as many more ossicles as it required to com- 
plete the maximum number of the species, the younger joints being inserted 
next to the older ones, which are distinguished by their greater prominence. 
In the upper part of the stem, the joints of subsequent growth are readily 
recognized, in some species more so than in others; but toward the terminal 
end, where all ossicles attain almost an equal size, it is often difficult. The 
stem matured from the root up, and remained at the upper end permanently 
in a state of immaturity. 
The maximum number of internodal joints varies considerably among 
the species. There may be only one or two to the internode throughout 
the stem, or many more. The largest number observed in Paleozoic Cri- 
noids is about fourteen; but among recent Pentacrinide as many as forty- 
five have been counted, and as many as seventy in Mesozoic species. 
The internodes of some species begin at quite a distance from the calyx, 
while others have no internodal joints at all. The former is manifestly the 
ease in certain genera of the Ichthyocrinide, in which the upper part of the 
