Analysis of growth layers in the teeth of Tursiops truncatus using light microscopy, microradiography, and SEM

Preliminary results show microradiography and scanning electron microscopy (SEM) to be more accurate methods of accessing growth layer groups (GLGs) in the teeth of Tursiops truncatus than transmitted light microscopy. Microradiography shows the rhythmic deposition of mineral as alternating radiopaque and radiolucent layers. It improves the resolution of GLGs near the pulp cavity in older individuals, better than either SEM or light microscopy. SEM of etched sections show GLGs as ridges and grooves which are easily counted from the micrograph. SEM also shows GLGs to be composed of fine incremental layers of uniform size and number which may allow for more precise age determination. Accessory layers are usually hypomineralized layers within the hypermineralized layer of the GLG and are more readily distinguishable as such in SEM of etched sections and microradiographs than in thin sections viewed under transmitted light. The neonatal line is hypomineralized, appearing translucent under transmitted light, radiolucent in a microradiograph, and as a ridge in SEM. (PDF contains 6 pages.)

Eggs of British Meniscus midges (diptera;dixidae) observed by scanning electron microscopy

The egg of Dixella martinii is described for the first time. The eggs of the Dixidae are placed in three morphological groups: bulbous and meshed; streamlined and smooth; streamlined and minutely spiculated. Ten of the fourteen species known from Britain are placed in these groups. After a detailed description of the egg of D. martinii, the three morphological groups are described and scanning electron micrographs are provided.