1 66 H. C. BRADLEY. 



examined, and it seemed to be rather uniform in amount. It 

 was present in every tissue, and in the nephridial organs it was 

 really abundant. In most of the tissues it was not at all com- 

 parable to the amount present in the Unionidae, approximately 

 o.i per cent, or less of the dry material. It will be remembered 

 that the nephridial organs of Modiola modiolus are usually pig- 

 mented a dark brown in all of some fifty specimens examined 

 by us this brown pigmentation was prominent. It is possible 

 that this lamellibranch deposits manganese obtained with its 

 food in the nephridia in an attempt to excrete the element; 

 that it is in this case adventitious and analogous to deposits of 

 iron-containing pigment in mammalian tissues as the result of 

 pathological conditions. It is interesting to note however that 

 this marine mussel which stands morphologically fairly close to 

 the Unionidse, should appear to utilize the element so charac- 

 teristic of the latter family. 



It is our belief that other lamellibranchs will be found which, 

 like Pinna squamosa, the Unionidae and perhaps Modiola modi- 

 olus, utilize the element manganese in their metabolic processes. 

 Such a chemical relationship may be useful in suggesting the 

 lines of the evolutionary process which has led to the develop- 

 ment of the present forms. It is our expectation to continue 

 this line of investigation as opportunity permits. 



