The comparative ultrastructure of fish bone osteogenesis and resorption induced by scale removal was described in the osteocytic (cellular-boned) Carassius auratus and the anosteocytic (acellular-boned) Tilapia macrocephala. Osteocytes, present in osteocytic bone, were lacking in anosteocytic bone. In osteocytic bone the osteoblast secreted a collagenous preosseous matrix in which it became enmeshed and then was termed a preosteocyte. When the preosseous matrix mineralized, the preosteocyte was termed an osteocyte and was completely surrounded by bone. In anosteocytic bone the osteoblasts receded from the mineralizing front and never became trapped as osteocytes. During resorption, types A and B resorptive cells, present in both bone types, invaded the matrix and demineralized the osseous zone. These cells were characterized by large amounts of granular endoplasmic reticulum and intracellular inclusions containing crystal-like material. Although functionally similar to mammalian osteoclasts, these cells lacked a characteristic ruffled border and were not multinucleated. The osteocytes of cellular bone did not appear to be involved during demineralization.

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The sagitta otolithic membrane of Fundulus heteroclitus consists of two different zones. A structured zone (gelatinous layer), which usually exhibits a reticulated or honeycomb-like architecture, is composed of tightly arranged fibrous material and covers only the sensory region of the macula. The gelatinous layer extends from the otolith surface to the tips of the sensory hairs, and probably functions primarily as a mechanoreceptor. The arrangement of this zone is closely associated with specific overlying structural features of the otolith surface and may also influence the pattern of mineral deposition to some degree. A nonstructured zone (subcupular meshwork) consists of fibers in very loose networks and covers both sensory and nonsensory regions of the macula. Over the sensory region, some of this fibrous material extends from the epithelial surface, through pores in the gelatinous layer, to the surface of the overlying otolith. In the nonsensory region, fibers of the subcupular meshwork are relatively more numerous and extend around the peripheral margin of the otolith. Evidence is presented which suggests that the fibrous material of the subcupular meshwork is incorporated into the otolith as an organic matrix constituent. New aspects on the ultrastructure of the otolith are presented and discussed.

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Rates of growth of Coccolithus huxleyi were determined at 7, 12, 18, 24, and 27C and found to be highest at 18 and 24C. The mean minimum doubling time was about 19 hr. The Qlo of growth rates for the interval 7-l% was 2.95. The Qlo value was 1.66 in medium lacking Na2COs. The percentage of cells forming coccoliths was twofold to threefold greater at 18 and 24C than at 7 and 27C.Coccolith dimensions were significantly different at 12, 18, 24, and 27C. The width and length of the coccoliths and the length of the elements of the upper disc decreased progressively above 18C. In contrast, the width of the upper elements increased to a maximum at 24C. Abnormal coccoliths were produced at all temperatures and were minimal in number at 1%.