Self-insemination

The relevant literature has been reviewed by Williams McVicar (959), Nollen (599), Oshmarin Prokhova (609) and Smyth (802). Although the mechanical processes involved in insemination are well known, almost nothing is known regarding the physiology of this process or the fertilisation which results. There is no information as to whether in cestodes sexual maturation is co-ordinated by an internal, sexual endocrine system or whether external chemotactic attraction between worms takes place. Three types of sperm transfer are known (a) self-insemination (b) crossinsemination and (c) hypodermic insemination. 

That both self-insemination and cross-fertilisation can occur in the same worm has been demonstrated unequivocally by the elegant experiments of Nollen (599) with H. diminuta. He used sperm labelled with [3H]thymidine and transplanted worms back to rats either singly or in combinations of labelled and unlabelled worms. In eight single-worm transplants (Table 7.2), all worms inseminated themselves, as demonstrated by the presence of labelled sperm in the receptaculum. In mixed labelled and unlabelled worm transplants, the labelled worms cross-inseminated with 92% of the unlabelled worms present. 

Self-insemination in Echinococcus granulosus in vivo. Journal of Helminthology, 43 383-8. 

Reproductive processes of helminths are diverse. The adults are hermaphroditic (monoecious) or dioecious, requiring, in some cases, no fertilization, in others, self- or cross-fertilization in hermaphrodites or insemination of females by males. Reproduction by monoecious species is simplified since no mate finding is necessary. In those species where separated sexes exist, and in hermaphroditic species where cross-fertilization is preferred, various adaptations have increased the likelihood of worm pairing and mate finding in the host. 

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