. The Cambridge natural history. Zoology. LARVAL FORMS 607 Dipleurula. He named this one Pluteus (easel), from a fancied resemblance, when turned upside down, to a painter's easel. The same name was bestowed on the next type, to which it presents a superficial resemblance, and hence the distinguishing prefix " Ophio-" was added to the original name by Mortensen. (3) The Uchinopluteiis, the larva of the Echinoidea. This type is strikingly like the preceding one in possessing a very small prae-oral lobe and in having the processes of the ciliated ring supported by calcareous rods, but
. The Cambridge natural history. Zoology. LARVAL FORMS 607 Dipleurula. He named this one Pluteus (easel), from a fancied resemblance, when turned upside down, to a painter's easel. The same name was bestowed on the next type, to which it presents a superficial resemblance, and hence the distinguishing prefix " Ophio-" was added to the original name by Mortensen. (3) The Uchinopluteiis, the larva of the Echinoidea. This type is strikingly like the preceding one in possessing a very small prae-oral lobe and in having the processes of the ciliated ring supported by calcareous rods, but a close inspection of these shows that they do not exactly correspond to those of the Ophiopluteus. Thus we have prae-oral, postero-dorsal, and post- antero-latei-al arm post-oral arm. Fig. 285.— view of larva of Echinus escu- lentus. X 45. axil, ep. Anterior ciliated epau- lette ; ap, apical plate or larval brain ; echy rudiment of Sea- urchin ; , left an- terior coelom ; , larval oesophagus; , , as in Fig. 284 ; , posterior ciliated epaulette; r. a. c, right anterior coelom. oral processes (Fig. 285), but usually no postero-lateral process, and when it does occur it remains short. On the other hand, an antero-lateral process unrepresented in the Ophiopluteus is constantly present, and in its later stage the Echinopluteus develops, out of parts of the ciliated ring, horizontally-placed crescentic ridges of cilia, which are termed ciliated epaulettes (Fig. 285, ). There may even be, as in the larva of Echinus esculentus, a second posterior set of these (Fig. 285, ). In the older larva at the apex of the prae-oral lobe there is an ectodermic thickening, at the base of which are developed nerve-cells and nerve fibres constituting a larval brain (Fig. 285, ap). (4) The Auricularia, the larva of the Holothuroidea. This type strikingly resembles the Bipinnaria in its external features. The prae-oral lobe is well developed, and has
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
