The scolex is biradially constructed, the proglottides flattened, quadrangular and bilaterally symmetrical.
When this is reached, growth of the proglottides ceases.
As a general rule the ripe proglottides are detached in chains and replaced by others which in their turn become detached, the process being repeated for a year or so until the worm weakens and is cast out.
The Cestodes of Elasmobranch fish offer more convincing examples of independent growth of the proglottides, for these are often set free with only the male organs developed, and each attains twice the size of the parental strobila.
The form of the proglottides is most generally a rhombic or trapezoidal figure.