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XF.W YORK STATE MUSEUM 



A means was also early found whereby water was admitted to the 

 right and left anterior portions of the coelom and from the left 

 anterior coelom was developed the present water vascular sys- 

 tem. The amount of water passing- in and out of the stone 

 canal was not at first so great as that passing through the enteric 

 cavity and it is doubtful if it ever became so. A still smaller 

 amount might have been draw^n into the body through the geni- 

 tal pore or pores. The systems which allow of admission and 

 exit of sea water to any portion of the coelomic cavity may be 

 classed as coelomic respiratory systems. 



It has already been stated that the fluid contents of the coe- 

 lomic cavities, in very primitive forms, received their oxygen 

 supply through the ectoderm and during the development of a 

 thecal armor they maintained such direct osmotic interchange 

 either by means of invaginations of ectoderm or of evaginations 

 of mesoderm. The latter form is abundantly shown in the papu- 

 lae and podia of living Echinoderms. The respiratory process 

 in such cases depends almost wholly on osmotic interchange 

 through specialized portions of the ectoderm and in a wholly 

 negligible quantity to direct exchange of sea water through the 

 madreporite. Strictly speaking, the respiratory process, wdiereby 

 the coelomic fluids are given their oxygen and relieved of their 

 wastes, is epidermal and it will here be treated as such. The 

 following tabular form will show these synthetically determined 

 classes and also some probable modifications of them : 



TABLE I 



MODES OF ECHINODERM RESPIRATION 

 Specialization of plate stereom 



'' between regular tlie- 



Epidermal < 



Specialization at 

 plate angles and 

 along sutures ^ 



Unspecialized 



^ Invagination 



Evagination 



Alimentary 

 or enteric 



Coelomic 



Specialized. Respiratory trees 

 r Water-vascular system in part 



t 



Gonadial 



< 



cal plates 



between thecal plates 

 associated with food 

 y^ grooves 

 Papulae 



Podia 



