Medusan sentence example
- Cladonema still has the typical medusan structure, and is able to swim about, but in Clavatella the umbrella is so much reduced that swimming is no longer possible.
- Secondly, there is the evidence from the development, namely, the presence of the entocodon in the medusa-bud, a structure which, as explained above, can only be accounted for satisfactorily by derivation from a medusan type of organization.
- Amphinema is a medusan genus of unknown hydroid.
- Another medusan genus is Proboscidactyla.
- As in the Gymnoblastea, the difficulty of uniting the hydroid and medusan systems into one scheme of classification is very great in the present state of our knowledge.Advertisement
- Thus a bract may be regarded, with Haeckel, as a modified umbrella of a medusa, a siphon as its manubrium, and a tentacle as representing a medusan tentacle shifted in attachment from the margin to the sub-umbrella; or a siphon may be compared with a polyp, of which the single tentacle has become shifted so as to be attached to the coenosarc and so on.
- There remains only the third feature, the endodermal gonads, as an argument for uniting the Scyphomedusae with the Anthozoa, against which must be set all the peculiarities of medusan organization in which the Scyphomedusae resemble the Hydromedusae.
- In other cases, however, the medusa-individuals become sexually mature while still attached to the parent polyp, and are then not set free at all, but become appanages of the hydroid colony and undergo degenerative changes leading to reduction and even to complete obliteration of their original medusan structure.
- The gonophores of different hydroids differ greatly in structure from one another, and form a series showing degeneration of the medusa-individual, which is gradually stripped, as it were, of its characteristic features of medusan organization and finally reduced to the simplest structure.
- Oesophagus, stomach, radial canals, ring-canal and tentacle-canals, constitute together the gastrovascular system and are lined throughout by endoderm, which forms also a flat sheet of cells connecting the radial canals and ring canal together like a web; this is the so-called endoderm-lamella (e.l.), a most important feature of medusan morphology, the nature of which will be apparent when the development is described.Advertisement