In the middle of this slide a stiffly fitting brass disk is inserted, to which a small turn-table motion may be communicated by an attached arm, acted on by two fine opposing screws accessible to the astronomer; and by their means the " fixed web " may be rendered strictly parallel with the movable one.
A crystal or glass circular disk, more suited to the shape of the sacred wafer; this is mounted in a frame of golden rays, and the whole is supported by a stem and bases.
The ovary, of two carpels, is seated on a ring-like disk FIG.
The foot of the Pectinibranchia, unlike the simple muscular disk of the Isopleura and Aspidobranchia, is very often divided into lobes, a fore, middle and hind lobe (pro-, mesoand meta-podium, see figs.
A, A hydriform person giving rise to medusiform person by budding from th margin of the disk; B, free swimming medusa (Steenstrupia of Forbes) detached from the same, with manubrial genitali.