MONOGRAPH OF THE EXISTING CRINOIDS. 



197 



discoverable in the interspace system of the central part of the calcareous reticu- 

 lation. 



There is among the crinoiils, as in other animals, a pronounced lack of corre- 

 lation in the comparative development of the several organs and structures, and 

 also in the cessation of development consequent on incipient senescence. Tiie most 

 strikiag presentment of this is in regard to the skeletal system. In the early post- 



FlO. 127.— I'PPEB MIDDLE PORTION OF THE COLDMN OT A SPEnMEN OF TEMOCKBtlS SPRISGERt FROM THE 'WEST COAST OF 



India, .showinq the cirri arranged in regular -ftnioRLS on the nodals, which are separated by a constant 



NUMBER OF INTERNODALS. 



larval stages this shows a very considerable advance over the other body elements ; 

 but it never attains a fixed maturity. All tlirougli tlie life of tlie anunal it continues 

 to develop by accretion and by resorption, and tlie arms, except in rare cases, con- 

 tinue to add termmal segments until deatli occurs. After tlic adult stage is reached, 

 however, change takes place very slowly, and at a constantly <luninisiung rate. It 

 is mainly evidenced by an increase in the size and in tiie solidnrity of the compo- 

 nent elements, which gives old animals a peculiarly robust and rugged appearance. 



