الفهرس 
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Abstract
The present study has dealt with investigating the ontogenetic
development of the gastrointestinal tract (GIT) of the Egyptian toad, Bufo
regularis using four-fold different and integrative approaches, namely,
morphological, histological, ultrastructural and molecular. The two former
approaches were employed as a guide when conducting the latter.
1-1- Morphological investigation: This involved illustration and
description for the developing GIT using light microscopy.
Seven developmental stages were mainly considered including
larval, i.e. 42, premetamorphic, i.e. 50, prometamorphic, i.e. 55,
metamorphic, i.e. 60, post-metamorphic, i.e. 66, juvenile and
adult stages. Morphometric parameters were employed for
tracing the developmental changes in the length of both GIT and
the body of the stages under consideration. The investigation
revealed that the length of the GIT had the same attitude as the
body length and exhibited progressive increase until stage 55,
decreased sharply at stages 60 and 66, then increased
progressively at juvenile and adult stages.2- Histological investigation: The developmental changes in
the histology of the GIT were traced and described for certain
stages namely 42, 50, 55, 60, 66, juvenile and adult stages. HistoSummary
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morphometric parameters were employed for determining the
developmental changes in the GIT histology including the length,
diameter, wall thickness and height of mucosal folds.3- Ultrastructural investigation: This has been done using the
transmission electron microscope. The ultrastructure of the
anterior portion of the developing anterior part of the small
intestine was investigated for the developmental stages 42, 50,
55, 60, 63 and 66. The results of this investigation was in
accordance with the histological observations where the
developmental changes at the ultrastructural level were
correlated with the developmental phases in relation to the
metamorphic state. The most prominent ultrastructural features
were the appearance of apoptotic bodies/nuclei within the larval
epithelium at the metamorphic stages 60 & 63.4- Molecular investigation: This involved two parts:
A- Determination of DNA fragmentation: This has been done
for different GIT segments of the developmental stages 50,
55, 60, 63 & 66 where the presence of deoxyribonucleic acid
(DNA) ladder was determined. This molecular investigation
revealed that the metamorphic stages 60 & 63 displayed
extensive DNA laddering compared with the other larval 50
& 55 and post-metamorphic 66 developmental stages where
the DNA appeared intact with no sign of fragmentation.
However, the prometamorphic stage 55 exhibited some DNA
fragmentation.
B- Detection of DNA damage and measurement of cell cycle
analysis: This has been done using flow cytometry and
applied on the whole small intestine of the developmental
stages 50, 55, 60, 63 & 66