Ultrastructure and Stereology of the Eggshell in Cnemidophorus sexlineatus (Lacertilia: Teiidae)

Abstract

The eggshell structure of the teiid lizard, Cnemidophorus sexlineatus, was examined by light and electron microscopy. Three distinct zones of the eggshell were recognized. In the innermost zone (Z,), which comprised 13% of the shell volume, fibrils were significantly more dense (less intrafibrillar space) than in the other two zones. The volume of interfibrillar space to fibrillar volume was equal. The fibrils in Zi were equal in size to those of the middle zone (Z,). Fibrils in Z2 were less dense (more intrafibrillar space) than those of Z,. There was significantly more fibrillar volume (59%) relative to interfibrillar space volume (41%) in Z,; Z2 comprised 61% of the total eggshell volume. Fibrils of the outermost zone (Z,) were significantly smaller in size than those of Z, or Z,, but did not change in fibrillar density (compactness of individual fibrils) from fibrils in Z2. There was a significant decrease in the proportional volume of the fibrilinterfibrillar space in Z, compared to Z,; both (fibril and space) occupied equal volume in Z,. Zone 3 occupied 26% of the total eggshell volume. Based on actual volume measurements, the fibrils in Zi were 1.3 times more dense than fibrils in Z, and 4.5 times more dense than fibrils in Z,. The fibrils of Z, contributed 5 times as much mass to total eggshell volume as did fibrils in Z, and 3 times as much mass as contributed by fibrils in Z,.