In order to prove the existence of the mitochondria and examine the relation between the motility of paraspermatozoa and mitochondria activity in the paraspermatozoa of Cipangoparudina japonica , the specimen was administered the vital staining by rhodamine which adheres to the activated mitochondria selectively, and were investigated by a fluorescence microscopy. As a result, the activated mitochondria existed in the region of rear 1/3 - 1/2 of the middle piece in paraspermatozoa. Moreover, the mitochondria activity was detected also in the paraspermatozoon which was not moving, indicating that the motility of paraspermatozoa is suppressed by some factor(s) in spite of the produce of ATP as the energy of the motility.
　Furthermore, concerning the action of Ca2+ and K+ as the factors which participate in the adjustment of the motility of paraspermatozoa, the time-dependent changes in the degree of motility (the number of spermatozoa which are moving/the all number of the spermatozoa) of small- and large-sized parasperematozoa maintained in the solution adjusted at various densities of both ions were examined. The results indicated that K+ is effective to raise the degree of the paraspermatozoon motility, and Ca2+ is necessary to activate the paraspermatozoa, while the motility of paraspermatozoa was completely suppressed at hyper concentration of Ca^2+.