40 THE CEINOIDEA CAMEEATA OF NOETH AMEEICA. 



crinus and Calamocrinus, and in all Ichtliyocrinidgo, so far as observed, the 

 new nodal joints were formed beneath the top joint, and the latter remained 

 permanently attached to the calyx. In Apiocrinus, 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 interhodal 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 j9<2n 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 Palaeozoic Cri- 

 noids is about fourteen ; but among recent Pentacrinidae 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 

 case in certain genera of the IchthyocrinidaB, in which the upper part of the 



