ECOLOGICL ASPECTS OF THE MORPHODYNAMICS OF SOME HYDROZOA

The specific architecture of a Hydroid polyp or a colony is,morphologically speaking, not a stable entity, because it issubjected to an incessant turnover and renewal at both cellularand higher levels. A continuous morphogenetic activity is inmany cases (e.g., Hydra) necessary for the maintenance of theshape and size of the individual polyp, because it has to compensatean equally continuous loss of cells at the level of the tentaclesand at the base of the polyp. Colonial species, such as Tubularia,Campanularia, and others, show regression-replacement cycles,some of which are conditioned by endogenous factors, while othersare released by ecological factors, such as environmental stresses.In all these morphodynamic events, regeneration plays an importantpart. It is an expression of the morphogenetic plasticity ofthe hydroid polyp, just as is asexual reproduction, anothercategory of morphodynamic elforts these organisms are subjectedto.     

Gametogenesis in the Genus Hydra

This paper comments on the induction of gametogenesis, on microscopicaland electronmicroscopical aspects of spermatogenesis and oogenesisand on fertilization in the genus Hydra. Spermiogenesis doesnot present any peculiarities. The ripe sperm contains no detectableacrosoinc. Egg-formation involves phagocytosis of entire oogoniaby growing oocytes. Several oocytes merge to a single oocyte,in which one nucleus becomes the germinal vesicle. The egg shellis formed only when the egg is fertilized. Various factors suchas the synchronization of gametogenesis, the length of sexualperiods, continuous release of sperm and the long life spanof sperm are considered to guarantee the fertilization of theeggs.