This tree acquires large dimensions, the trunk being often from 4 to 6 ft.
The endoderm of the planula now acquires a cavity, and at the narrower pole a mouth is formed, giving rise to the primary siphon.
When exposed in the moist condition to the air it gradually acquires a red colour.
As an example of the former it has been shown (Beddard) that a large median sac in Lybiodrilus is at first freely open to the coelom, that it later becomes shut off from the same, that it then acquires an external orifice, and, finally, that it encloses the ovary or ovaries, between which and the exterior a passage is thus effected.
It has simply been traced as far as the formation of a diblastula which acquires a ciliated band, and becomes a nearly spherical trochosphere.