Vol. XL VIII. June, 1925. No. 6. 



BIOLOGICAL BULLETIN 



RESPIRATORY DIFFERENCES ALONG THE AXIS OF 

 THE SPONGE GRANTIA. 



LIBBIE H. HYMAX 

 I!- LI. XOOLOGICAL LABORATORY, UNIVERSITY OF CHICAGO. 



I >itlcrenccs in the rate of respiratory metabolism along the 

 principal axis have now been demonstrated for a number of 

 animal-: fur the hydroid Corymorpha (Child, '23, Hyman, '230), 

 l"i tin- ine<lu-a Cassiopaea (McClendon, '17), for Planaria 

 1 1\ in. in. '-?V>)i and for several annelids (Hyman and Gali^her, 

 'ji . Ki-cently Shearer ('24) has reported similar results for the 

 chick embryo and the earthworm. Unfortunately in Shear 

 \\ork n -ions of very dilTerent morphological constitution \\< n 

 ' "injured and it is therefore doubtful if his results can be 



ltd as lending support to the physiological gradient concep- 

 tion, lor example anterior and posterior halves of the chick 

 cml'iAo in the stages studied by Shearer differ enormously in 

 their content of nervous tissue, due to the presence of the brain 

 and chid sense organs in the anterior half. The much greater 

 iv-pi ratory rate of the anterior half reported by Shearer is 

 l>i"lul>ly largely due to the greater proportion of nervous tissue 

 which it contains. Similarly in the earthworm the mature head 

 i- morphologically and functionally dilTerent from the rest of 

 the body and re>j>irutory differences between it and other regions 

 must be in jiart due to such specific differences. In brief, 

 Shearcr'> measurements concern not the gradient itself but the 

 secondary differentiations associated with the gradient. Shearer 

 also seems to be unaware of the existence in annelids (and in the 

 early embryos of vertebrates) of the double type of gradient 

 (.Hyman and C.alijier, '17) and the pieces of the earthworm 

 which he compared were consequently not correctly chosen and 

 ' neither to prove nor disprove the existence in this animal 



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