[Etymological confusion in Japanese terms for the testis: past and present]

In Japan, two scientific words are used for the testis, SEISO and KOGAN. SEISO is the word accepted by most of the bioscience societies and etymologically means the nest of sperms. KOGAN, is a word of Chinese origin and mainly used by urologists. Its etymologic meaning is unclear. About one to two hundreds years ago, many classical Japanese books of medicine used EKIGAN the Chinese character of which is quite similar to KOGAN, and which etymologically was described as "pleasure balls of man" by a contemporary anatomist in Japan, although I presume it was intended to mean "a couple of balls, side by side". In order to avoid terminologic confusion, SEISO, the standard word used in many academic fields, is recommended for universal use not only in scientific papers but in daily language in Japan.