- Section of a Statocyst and on a freely - projecting Ocellus of Tiaropsis diademata; cf.
The simple form of ocellus described in the foregoing paragraph may become folded into a pit or cup, the interior of which becomes filled with a clear gelatinous secretion forming a sort of vitreous Modified after Linko, Travaux Soc. Imp. Nat., St.
Besides the ordinary type of ocellus just described, there is found in one genus (Tiaropsis) a type of ocellus in which the visual elements Si are inverted, and have their cones Sub jj "'` * turned away from '` the light, as in the 4V5:40--* ?? ?` ' ahuman retina (fig.
A similar ocellus is formed in Aurelia among the Scyphomedusae (q.v.).
- Ocellus of Lizzia koellikeri.
Ocellus Lucanus >>
Ocellus, and en, internal canal of the tentaculocyst.
In Aurelia there are two on each rhopalium, a simple ocellus on the exumbral side, and a cupped ocellus on the subumbral side (not present in young individuals).
7); on the exumbral aspect there are two median ocelli (oc l, oc 2), a distal and a proximal, each of them a vesiculate ocellus with a lens, and on the sides of the rhopalium are two pairs of ocelli without lenses (oc. 1); sometimes also an additional seventh ocellus occurs, a pit-like structure without a lens, either between the two median ocelli, or placed asymmetrically near the median proximal ocellus.
The simplest type of ocellus is exemplified by the exumbral ocellus of Aurelia, a simple patch of pigment-cells interspersed with visual cells, the whole on a level with the remaining ectodermal epithelium.
In the next stage of complication, seen in the supernumerary (seventh) ocellus of Charybdaea, the patch of pigmented and sensory epithelium is pushed in to form a little pit, in the T Aurelia aurita.
In this way the ocellus becomes a true eye, very similar in plan to the eyes of Gastropods and other molluscs.
The subumbral ocellus of Aurelia is found to be of the inverted type, with the visual cones turned away from the light, as in Tiaropsis amongst Hydromedusae, and here also the pigment is furnished by the endoderm, forming a cup into which the ectodermal visual cells project (Schewiakoff ['31) In) the Stauromedusae tentaculocysts are either absent altogether, as in - St.
The basal por tion bears an ocellus (oc) of > ' '--OtOZ ' simple structure.
- Vertical section of the Median Distal Ocellus (oc t of the preceding figure) of Charybdaea.