THE MYXO.SPORIDIA, OK PSOKOSPERMS OF FISHES. 109 



These data may be summarized as follows: ^ 



'Occurrences." 



Total* 



In excretory tract 



In nonexcretory tract 



* Omitting the dubious "kidney" species and occurrences, and-the somewhat 

 questionable occurrence of Myxobolus ellipsoides in the gall bladder. 



ORGANAL DISTRIBUTION OF THE VACUOLE. 



From an examination of the above table it will be seen that the range 

 of the genus Myxoholus throughout the organs is a wide one, hut that it 

 is almost strictly complementary to that of the Chloromyxidcc, Gystodis- 

 cidw, and Myxidlidoi. 



The real significance of these peculiarities of organ al distribution 

 lies, however, not so much in the peculiarities of generic-organal distri- 

 bution, interesting as these are, as in the tact that these limits of the- 

 distribution of the genera in the organs almost exactly coincide ivith the 

 limits of the 'presence of the iodinophile vacuole in the subclass^ nearly all 

 of the nonvacuolate Fhcenocystes being confined to the excretory tract, 

 while nearly all the vacuolate Phmnocystes are absent from this tract. 



Two questions immediately suggest themselves: 



1. Is it possible that the function of the vacuole is here even remotely 

 shadowed? The constancy of the vacuole in the spore and the incon- 

 stancy of vacuoles ( ? genetically related ) in the myxosporidium would 

 seem to indicate that it functions during the spore stage. One sup- 

 position which suggests itself is that in some way it might subserve 

 oxygenation, but it is more probable that it serves as a food reservoir 

 for the sporoplasm (cf. Thelohan's comparison of its micro-chemical 

 reactions with those of glycogen ; p. 208 ). Unfortunately the origin of 

 the structure and the phenomena of its disappearance after the exit of 

 the sporoplasm have not been worked out. 



i If the dubious occnxvQnaQ oi Mijxobolus elUpsoides in tlie gall bladder be excluded 

 as not proven. In any case the exceptionally wide organal range of this species 

 should be considered in estinuitiug the value of its occurrence in unusual seats. 



