Abstract:
We determined the sources of calcium for the developing embryo and the parallel changes in eggshell structure in the Indian agamid lizard Psammophilus blanfordanus. The developing eggs were opened at 0 (freshly laid), 10, 20, 30, 35, 38, and 40 days of incubation and at hatching (day 41) and subjected to chemical and structural analyses. The oval and flexible-shelled eggs had undergone significant changes in size (40% increase in length, 68% increase in breadth and 315% increase in weight) from laying to hatching. The fresh eggshell contained 2.76 mg (12.51%) calcium whereas the hatched eggshell had only 1.02 mg (7.20%), or a 63% reduction from its original content. The yolk + fluids fraction provides only 0.47 mg to the 1.76 mg of calcium in the hatchling, the rest being resorbed from the eggshell during development. The fresh eggshell (62 mu m thick) had a rough granular structure in its calcareous layer with near uniform rectangular/polygonal fields made up of globules of varying sizes. The membrane layer had a multilayered mat of interwoven, irregularly oriented and bifurcated, fibres of uneven thickness. The spherical globules were absent at several places in the hatched eggshell as a result of eggshell calcium utilisation by the developing embryo. Hence, like that of most reptiles, the eggshell of Psammophilus blanfordanus also acts as a secondary source of calcium for the developing embryo. The embryo utilizes the eggshell calcium towards the end of development.