Balfour put forward the view that the polyp was the more primitive type, and that the medusa is a special modification of the polyp for reproductive purposes, the result of division of labour in a polypcolony, whereby special reproductive persons become detached and acquire organs of locomotion for spreading the species.
Many views have been put forward as to the morphological relationship between the two types of person in the Hydromedusae.
On this point the following theories have been put forward.
A natural classification of the Hydroidea has yet to be put forward.
Among the earliest of these speculations is that put forward by Benoit de Maillet in his Telliained, which, though printed in 1735, was not published until twenty-three years later.