THE CELLULAR ELEMENTS IN THE PERI VISCERAL 

 FLUID OF ECHINODERMS. 



JAMES ERNEST KINDRED, 

 BIOLOGICAL LABORATORY, WESTERN RESERVE UNIVERSITY. 



A consideration of the cellular elements in an animal group, 

 particularly those cellular elements which are present in cavities 

 derived from the primitive ccelom, should include references to 

 the origin of these cells and any other factors which may be con- 

 cerned with their modifications, such as the habits, the powers of 

 regeneration and the topographical anatomy of the organ sys- 

 tems of the animals examined. It is generally conceded from 

 the evidences of palaeontology and comparative embryology that 

 the Echinoderms of to-day are a fairly ancient group which have 

 been able to adapt themselves to diverse environmental changes. 

 The same pentaradial symmetry is present in all of them, al- 

 though masked in some, but the principal variations which are 

 characteristic of the classes are concerned primarily with the 

 character of the body wall and secondarily with the distribution 

 of the breathing organs. In the Echinoderms we can distinguish 

 three types of organization of the body wall and breathing organs: 

 the first type is characterized by a fairly flexible body and diffuse 

 breathing organs (e.g., Asteroidea and Ophiuroi'dea), the second 

 by a rigid test and limited breathing organs (e.g., Echinoidea), 

 and the third by a well-developed muscular body wall and limited 

 breathing organs (e.g., Holothuroidea). In all of the classes 

 except the Holothuroidea, the movements of the body are very 

 sluggish, consequently the oxygen requirements for muscular 

 activity are very low and a system for rapid transfer of oxygen is 

 not needed. But in the majority of the Holothuroidea, the de- 

 velopment of muscle necessitates a great available supply of free 

 oxygen and a mechanism for carrying this oxygen must be present. 

 Therefore one phase of this investigation will attempt to corre- 

 late the appearance of different types of evils in the perivisceral 

 fluid with the character of the body wall, the distribution of the 



breathing organs and the movements of the body as a whole. 



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