Felix,
Check out Joly's Legendsin Japanese Art page 195.
" It is said that the female conceives by running on the waves on the 18th day of the 8th moon, if the sky is clear, or by ...( some foreplay which I don't think the censor will appreciate, so i won't even try ).
Or............. for those more " learned ", as pointed out by Nobody san, there's this totally dull entry that involved the Bonze of kencho-ji, Jikyu Zosu, visiting Chikubujima in Omi and had this moment..........alluding to some Chinese poem of old about tree, rabbit running on waves, holy lights and beginning of time and such.
See Afu Quarterly ( Summer issue ) page 78-79.
milt