It also excludes the more evident double terata, and, of course, the cases of duplication of the female genital organs (double clitoris, vulva, vagina, and uterus).
Although Schurig, Meckel, Himly, Taruffi, and others give bibliographic lists of diphallic terata, even in them erroneous references are common, and there is evidence to show that many cases have been duplicated under different names.

Ballantyne and Skirving have consulted all the older original references available and eliminated duplications of reports and, adhering to their original definition, have collected and described individually 20 cases; they offer the following conclusions:-- 1.

Diphallus, or duplication of the penis in an otherwise apparently single individual, is a very rare anomaly, records of only 20 cases having been found in a fairly exhaustive search through teratologic literature.

As a distinct and well-authenticated type it has only quite recently been recognized by teratologists.
2.

It does not of itself interfere with intrauterine or extrauterine life; but the associated anomalies (e.g., atresia ani) may be sources of danger.