In some cases, any polyp of the colony may bud medusae; in other cases, only certain polyps, the blastostyles, have this power.
When blastostyles are present, however, they are never enclosed FIG.
Trophosome encrusting with hydranths of Bougainvillea-type, polyps differentiated into blastostyles, gastrozoids and dactylozoids; gonosome free medusae or gonophores.
The medusa-buds, as already stated, are always produced from blastostyles, reduced non-nutritive polyps without mouth or tentacles.
The blastostyles, gonophores and gonothecae furnish a series of variations which can best be considered as so many stages of evolution.
Each corbula contains a central row of blastostyles enclosed and protected by lateral rows of branches representing stunted buds (Allman , p. 60, fig.
Gonostyles, appendages which produce by budding medusae or gonophores, like the blastostyles of a hydroid colony.
The gonostyles have been compared to the blastostyles of a hydroid colony, or to the manubrium of a medusa which produces free or sessile medusa-buds.