Mating with a partner is more desirable biologically, as the genetic material of the resultant offspring is varied, but if mating with a partner is not possible, self-fertilization is practiced. The male sexual organ of an adult banana slug is quite large in proportion to its size, as well as compared to the female organ. It is possible for banana slugs, while mating, to become stuck together. If a substantial amount of wiggling fails to separate them, the male organ will be bitten off (using the slugs radula), see apophallation. If a banana slug has lost its male sexual organ, it can still mate as a female, making its hermaphroditic quality a valuable adaptation. The species of colourful sea slugs Goniobranchus reticulatus is hermaphroditic, with both male and female organs active at the same time during copulation. After mating, the external portion of the penis detaches, but is able to regrow within 24 hours. Hamlets, unlike other fish, seem quite at ease mating in front of divers, allowing observations in the wild to occur readily. They do not practice self-fertilization, but when they find a mate, the pair takes turns between which one acts as the male and which acts as the female through multiple matings, usually over the course of several nights. Earthworms are another example of a simultaneous hermaphrodite. Although they possess ovaries and testes, they have a protective mechanism against self-fertilization. Sexual reproduction occurs when two worms meet and exchange gametes, copulating on damp nights during warm seasons.
The rare neoplasms generally do not follow a determinate development path and are often difficult to diagnose.Histologically, these malignant mixed tumours have epithelial and mesenchymal components and are very large, nodular, circumscribed, and nonulcerated. They are morphologically identical to pleomorphic adenoma and have a female predilection. They range from developing deep dermal to subcutaneous nodules and metastasise at a very high rate. Malignant mixed tumours can emerge "de nova or more rarely develop from a cartilaginous syringoma. "(IADVL, 2004)

Causes
Currently malignant mixed tumours do not have a definitive predisposing factor; however, prior physical injury has been proposed as a potential risk for the emergence of these tumours. Chondroid syringoma less than three centimetres are shown to have a heightened risk of malignancy. Other critical indicators include excessive mucoid matrix, – a connective tissue tumour with a myxoid background that is composed of "clear, mucoid substance – numerous mitoses, and poorly differentiated chondroid components." (Metzler, Schaumburg-Lever, Hornstein, and Rassner, 1996)

Diagnosis
Diagnosing malignant mixed tumours is difficult as there many types of tumours and their variants. Malignant chondroid syringoma is particularly challenging to distinguish from other skin tumours as it is prone to the absence of definitive symptoms and an ambiguous clinical presentation. Some signs that help determine diagnosis of malignancy include: "mitosis, nuclear atypia, pleomorphism, lymphatic invasion, and local recurrence" (IADVL, 2004). Though it is usually found within women in the forties, the youngest-recorded case was fourteen years old and the oldest was eighty-six.