. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CRYSTAL ORIENTATION IN THE APICAL PLATES OF ABERRANT ECHINOIDS DAVID M. RAUP AND EMERY F. SWAN Department of Geological Sciences, University of Rochester, Rochester, New York 14627; Department of Zoology, University of Nciv Hampshire, Durham, Nevv Hampshire 03824, and Museum of Comparative Zoology, Harvard University, Cambridge, Mass. The arrangement of skeletal parts in the echinoids is of such regularity that the parts can be assigned an identifying combination of names, numbers and letters. In the regular urchins the peri
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CRYSTAL ORIENTATION IN THE APICAL PLATES OF ABERRANT ECHINOIDS DAVID M. RAUP AND EMERY F. SWAN Department of Geological Sciences, University of Rochester, Rochester, New York 14627; Department of Zoology, University of Nciv Hampshire, Durham, Nevv Hampshire 03824, and Museum of Comparative Zoology, Harvard University, Cambridge, Mass. The arrangement of skeletal parts in the echinoids is of such regularity that the parts can be assigned an identifying combination of names, numbers and letters. In the regular urchins the periproct enclosing the anus is located at the aboral apex and around it are the five genital plates alternating with the five ocular plates. Although there is some question concerning the premises Loven (1874) used in setting it up, his system for numbering these plates is now almost universally used by students of these animals. The landmark in the system is the madreporite, a modified genital plate. The genital plates are numbered with Arabic numerals 1 through 5 counterclockwise as one looks down on the apex, with the madreporite assigned number 2. The ocular plates are assigned Roman numerals and precede their genital counterparts in the counterclockwise sequence as shown in figure 1. In the genus Strongylocentrotus it is usual for ocular plates I and V to abut the periproct separating the adjacent genital plates from each other. Such ocular plates are termed "insert" (Jackson, 1912). The bases of the other ocular plates are usually occluded from the periproct by the abutting bases of the genital plates beside them and are called "exsert" according to Jackson's terminology. G-2 o-m o-n G-3 o-rz. G-2 o-m o-n G-I G-3 o-i O-ffi G-4 G-5 a. o-z. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
