الفهرس 
ACKNOWLEDGEMENTSOnly 14 pages are availabe for public view
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Abstract
The present study aimed to investigate the morphological features of caeca during the pre- and post-hatching periods of the development of Japanese quails (Coturnix coturnix japonica) using light and electron microscopy.
Gross morphology indicated that caeca as double projection. They led in both sides of the ileum and cranial to the colon. The caeca had increased in length and diameter with the advancement of age.
Histologically, primitive hindgut appeared as a tube and caeca arose as bilateral invagination in hindgut mucosa that continued to separate until appeared as bilateral swelling on both ventrolateral sides of the hindgut wall from ED 2 until ED 4. from ED 5, caeca could be dissected from the ileocaeco-colic junction to the distal part of caeca with the ileum. Through ED 5 and ED 7, caeca appeared to have unfolded mucosa layer along their length. The mucosal folds began to appear and differ in number and shape along its length at ED 9. Proximal, middle and distal parts had different shapes of villi through pre-hatching development while after hatching, distinct villi in the proximal part and plicae with short mucosal folds in middle and distal parts were demonstrated.
Ileocaeco-colic junction was seen in three levels, connected with colon in the mucosa layer and with ileum in the muscle and serosa layers. Caeca, through the ICC junction at early embryonic stages, had unfolded mucosa layer consisted of pseudostratified columnar epithelium. from ED 13 to after hatching, different shapes of villi appeared through the three levels. Tongue shaped villi, filled with lymphatic tissue that was lined by simple cuboidal epithelium, were seen through the second and last junction levels.
Goblet cells showed a positive reaction to PAS at ED 13 in the proximal part while in the ICC junction, middle and distal parts, they were less prominent. After hatching, goblet cells were clearly seen in the ICC junction and proximal part while they decreased in number in middle and distal parts.
Rodlet cells showed a positive reaction to BB appeared in the epithelium of the proximal part of ED8 by semithin sections, while from ED 13 in middle and distal parts by light microscopy.
The current study demonstrated that there was no CTs in lamina propria of the caeca of quail in pre-hatching life till two post-hatching weeks. However, diffuse lymphatic tissues were observed in lamina propria throughout the caecal wall in growing (from ED 13) and adult birds.
Immature M cells were found at ED 13 associated with surface epithelium of villi, had a columnar shape with short and irregular microvilli and were connected with the neighboring epithelial cells by desmosomes. M cells possessed dark cytoplasm with rER and mitochondria. Its nuclei were large and possessed little heterochromatin with two distinct nucleoli.
Primordia of caecal glands were observed at ED 8 and crypts of Lieberkühn had a very distinct shape on ED 13. Neuroendocrine cells were also seen at hatching day at the basement membrane of epithelium with a large nucleus and scattered dense granules.
Submucosa layer appeared as loose connective tissue containing some immune cells like macrophages, dendritic cells, lymphocytes and white blood cells in ED 8 and by development, aggregations of lymphocytes and other immune cells as in ED 13.
Developed muscle layer appeared as a thin outer longitudinal and thick inner circular smooth muscle fibers integrated by connective tissue, telocytes and fat cells on ED 11. Bundles of nerve fibers were seen in between the two layers of muscularis. The present study is the first one to highlight on TCs distribution in the quail caecum that appeared from the ED 13.