In the Calyptoblastea the perisarc is always continued above the From Allman's Gymnoblastic Hydroids, by permission of the Council of the Ray Society.
The buds may all become detached after a time and give rise to separate and independent individuals, as in the common Hydra, in which only polyp-individuals are produced and sexual elements From Allman's Gymnoblastic Hydroids, by permission of are developed the Council of the Ray Society.
Hence, in a colony of gymnoblastic hydroids, the oldest polyp of each system, that is to say, of the main stem or of a branch, is the topmost polyp; II ?a ` FIG.
The gymnoblastic polyp usually has a distinct perisarc investing the hydrorhiza and the hydrocaulus, sometimes also the hydranth as far as the bases of the tentacles (Bimeria); but in such cases the perisarc forms a closely-fitting investment or cuticule on the hydranth, never a hydrotheca standing off from it, as in the next sub-order.
In some species of the genus Cunina (Narcomedusae) the youngest individuals (actinulae) are parasitic on other medusae (see below), but in later life the parasitic From Allman's Gymnoblastic Hydroids, by permission of habit is abandoned.