. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. 36 MEDUSA. II. exj. end. I. â sub ait. ooc prob. gonads begin to develop. In the female medusa only a small number of eggs are developed; these eggs are fertilized whUe still sitting on the manubrium, and here they de\-elop into actinula lar\'ae, which are not liberated until two wreaths of tentacles are present. Asexual reproduction may continue some time after sexual reproduction has commenced, but soon ceases. It is unknown, whether the first medusae, liberated directly from the hydroid
. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. 36 MEDUSA. II. exj. end. I. â sub ait. ooc prob. gonads begin to develop. In the female medusa only a small number of eggs are developed; these eggs are fertilized whUe still sitting on the manubrium, and here they de\-elop into actinula lar\'ae, which are not liberated until two wreaths of tentacles are present. Asexual reproduction may continue some time after sexual reproduction has commenced, but soon ceases. It is unknown, whether the first medusae, liberated directly from the hydroid, ever reach sexual maturity, or. whether this stage is reserv'ed for later generations. Not until 3 or 4 months after the appearance of the first medusae in the plankton, the first cases of sexual reproduction are observed, but shortly afterwards practically no budding individuals are found. The time at which the sexual reproduction begins, depends on the age of the stock, not on the age of the single in- dividuals. Remarks on the morphology. The general shape of this medusa is well-known, and I sliall, therefore, be content to put forth some few additional remarks. â The nettle-cell arma- ture of the mouth: At quite a short distance ab(n-e tJie mouth opening the lower end of the mouth tulie is surrounded by a highly prominent, ring-shaped mound of nematocyst-bearing ectoderm (longitudinal section, textfig. 29); it is compound of several Fig. 29. Hybocodon proli/er. Jâ . ncmatocyst ring; ooc. remains of oocytes not yet devoured by the plas- modial egg; pt. lobes of egg; sub. subumbrella; Ir. transitional zone of partly vacuolated endodermal cells; vac. vacuolated endodermal cells of manubrium ("Chordazellen").â rOUnded knobs (see transversal Section, textfig. 30), act. young actinula; ectodermal epithelium and supporting la- mella fully developed; the latter is very thin in the proximal part; endodermal epitheUum developed only in the prox
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Keywords: ., bookcentury1800, bookdecade1890, booksu, booksubjectarcticregions
