Usually they open into a median vagina, formed by an ectodermal inpushing and lined with chitin.
Thus the ectodermal rim runs round the edge of each lobe of the umbrella and then passes upwards towards the base of the tentacle from the re-entering angle between two adjacent lobes, to form with its fellow of the next lobe a tentacle-clasp or peronium, i.e.
It has been asserted that the tentaculocysts are entirely ectodermal and that either the family should be placed amongst the Leptomedusae, or should form, together with certain Leptomedusae, an entirely distinct order.
In the hydropolyp the ectodermal muscle-fibres are always directed longitudinally.
Haeckel regarded the whole structure as a glandular ectodermal pit formed on the exumbral surface of a medusa-person.
By a simple modification, the open pit becomes a solid ectodermal ingrowth, just as in Teleostean fishes the hollow medullary tube, or the auditory pit of other vertebrate embryos, is formed at first as a solid cord of cells, which acquires a cavity secondarily.
The ectodermal epithelium on the distal side of the bud becomes thickened, grows inwards, and forms a typical entocodon (fig.
The polyp (hydropolyp) is of simple structure, and never has an ectodermal oesophagus or mesenteries.
A large nematocyst, with everted thread, is seen in the right-hand ectodermal cell.
The characteristic sense-organs are ectodermal otocysts, absent, however, in some genera, in which case cordyli may replace them.