RENAL FUNCTION 271 



octopus and followed the changes of dye concentration in the urine. Though 

 the pattern of excretion varied from dye to dye, Bruni concluded that the 

 dyes were being excreted by filtration ; but, since he did not carry out 

 simultaneous analyses of blood and urine, we cannot rule out the proba- 

 bility that secretion was occurring. 



Harrison and Martin (1955) and Harrison (1954), using the dye 

 phenol red, have shown an active secretion of this substance which, as in 

 the gastropod, may be inhibited by DNP. 



Finally, for indirect proof of the secretion of inorganic materials claimed 

 by Mayer and Rathery, we may cite the analyses of Robertson ( 1953) on 

 blood and urine of the octopus from which he concludes : "The mechanism 

 of ionic regulation of the plasma in cephalopods involves the continuous 

 selective excretion of ions in the excretory fluids and controlled uptake of 

 ions by the permeable surfaces." 



From the experiments which have been described on molluscs it should 

 be clear that substances which are actively transported and which require 

 no chemical changes in their transport may be very advantageously studied 

 in this phylum. Much work remains to be done to demonstrate what ma- 

 terials are transported and how their rates vary both independently and 

 in competition with each other. It is to be hoped that such systems may 

 be studied not only for the knowledge as it applies to this phylum, but that 

 some of these systems may be employed in the larger task of demonstrating 

 the specific cellular mechanisms of transport. 



Arthropods 



If we examine once again the paper of Maluf (1941b) on urine forma- 

 tion in the crayfish we find satisfactory evidence of the secretion of cyanol, 

 a dye which he reports is not handled by the vertebrate kidney. Though 

 his work was not done on a strictly quantitative basis, it is clear from the 

 observation that the dye was many times as concentrated in the urine as 

 in the blood that secretion was occurring. The study included a dye which 

 is handled by the vertebrate kidney and the secretion of this dye, phenol 

 red, was judged to be at about one-half the rate of cyanol. Neutral red 

 appeared in the urine but did not appear to be concentrated there. These 

 data confirm secretion but do not answer the profound question : Are all 

 the components of crayfish urine secreted? 



One of the crucial points on which a decision would rest would certainly 

 be the secretion of water. In a somewhat earlier paper Maluf (1941a) 

 reported cytological evidence in Camharus for the secretion of water. It 

 had been established already at this time that the urine is hypotonic to the 

 blood. Of the alternative explanations Maluf preferred that in which all 

 the constituents of the urine are secreted, the water being secreted in 



