. Elementary text-book of zoology. Zoology. IfTDEO/OA. 237 be separated as an independent layer of nucleated fibre cells below the epithelium. The Polyps are not invariably alike, proliferous Polyps (or Blastostyles) being frequently found as well as the nutritive ones. The proliferous Polyps develop generative buds 011 their walls. The sterile Polyps may differ from one another in the number of tentacles and in their entire form, so that different kinds of individuals may be found on a single stock. Thus we rind the polymorphism of the- Siphonophora foreshadowed amongst the Hydroidea (Podocor
. Elementary text-book of zoology. Zoology. IfTDEO/OA. 237 be separated as an independent layer of nucleated fibre cells below the epithelium. The Polyps are not invariably alike, proliferous Polyps (or Blastostyles) being frequently found as well as the nutritive ones. The proliferous Polyps develop generative buds 011 their walls. The sterile Polyps may differ from one another in the number of tentacles and in their entire form, so that different kinds of individuals may be found on a single stock. Thus we rind the polymorphism of the- Siphonophora foreshadowed amongst the Hydroidea (Podocoryne, Plumularia). The generative products are only exceptionally developed in the Polyp body itself, in which case they are produced in the ecto- derm (Hydra}. This exception is probably to be looked upon as an extreme case of degeneration of a medusoid bud. As a rule the generative products are de- veloped in special medusoid buds [gono- phores] formed from both cell-layers. In the most simple cases the budding in- dividuals of the sexual generation contain a. PIG. 181.—Podocoryne cariiea (after C. Grobben). P, Polyp ; -I/, Medusa bud on the proliferating polyp; &', spiral- zooid; Sk, skeleton Polyp (compare the free Medusa, fio-. 154). diverticulum of the gastric "cavity of the polyp-shaped parent or of the axial cavity of the hydroid stock. The generative products become accumulated around 'this diverticulum (Hydractirtia echinata, Claim squaxiata}. In a more advanced stage we rind a mantle-like envelope enclosing the bud, and con- stituting the rudiment of the umbrella, with a continuous vascular lamella or with more or less developed radial vessels (Tubularia coronata, Eudendrium ramosum, Van Ben.) Finally, at the highest stage, the buds develop into small Medusa? (Campanularia yelatinosa van Ben., tfarsia tubutosa), which become free, and sooner or later,. Please note that these images are extracted from scanned page images that may have been digitally enhanced
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
