ABSTRACThe present investigation aims to illustrate the histological and ultrastructural differences of the liver and pancreas of a carnivorous fish, Schilbe mystus, and a herbivorous fish, Labeo niloticus. The histological examination of the liver of both studied species revealed that the liver is mainly composed of a continuous compact field of the hepatocytes. The hepatocyte-sinusoidal structure of the liver of Schilbe mystus consists of the solid form and tubular one, while that of Labeo niloticus consists of the tubular form and cord-like one.The ultrastructural examination of the liver of both studied species revealed that it is composed mainly of hepatocytes, Kupffer (macrophages) and to (fat-storing) cells. The hepatocytes of Schilbe mystus are characterized by the presence of numerous glycogen rosettes, numerous lipid droplets and a rough endoplasmic reticulum, while those of Labeo niloticus are characterized by the presence of numerous glycogen rosettes, a few lipid droplets and a rough endoplasmic reticulum. The hepatocytes of both studied species possess numerous microvilli, which extend into the space of Disse or into the bile canaliculi lumina.In both studied species, there is a prominent perisinusoidal space between the hepatocytes and blood sinusoids, the space of Disse. This space usually contains the Ito cells, which are stellate in shape and are characterized by the presence of lipid droplets.The bile canaliculi of Schilbe mystus are of the intercellular type, while those of Labeo niloticus are of both the intercellular and intracellular types.The histological investigation of the pancreas of both studied species revealed that there are three types: the compact, disseminated and intrahepatic types. This pancreas showed that it consists of a highly lobulated gland of the compound acinar type. The acinar (pancreatic) cells are pyramidal in shape; they possess a basophilic cytoplasm and eosinophilic zymogenous secretory granules.The ultrastructural investigation of the acinar cells of both studied species revealed two cell types: the dark and light acinar cells. These cells are characterized by the presence of numerous zymogenous secretory granules and a well-developed rough endoplasmic reticulum.

he present investigation aims to illustrate the morphological, histological and ultrastructural differences in the intestine of a carnivorous fish, Schilbe mystus and a herbivorous fish, Labeo niloticus, in correlation with their feeding habits. The histological examination of the mucosa of the intestine of both studied species revealed that it is built up of a simple columnar epithelium that contains goblet cells. Though these, are generally more numerous in the intestine of Schilbe mystus than in that of Labeo niloticus. The ultrastructural investigation of the mucosa of the duodenum and ileum of Schilbe mystus revealed that the enterocytes are tall columnar cells and possess well-developed microvilli, numerous mitochondria, microtubules and numerous lipid droplets. The ultrastructural examination of the mucosa of the ileum of Labeo niloticus revealed that the enterocytes are tall columnar and possess well-developed microvilli, numerous mitochondria, microtubules, a few endocytotic channels and aggregated chylomicrons. The enterocytes of the rectum of both studied species are tall columnar and are characterized by the presence of short and wellspaced microvilli, a well-developed vesiculotubular system, numerous microtubules and mitochondria. In addition, the rectal enterocytes of Schilbe mystus contain endocytotic vesicles. The intestinal muscularis of both studied species is well-developed and built up of unstriated muscle fibres, which are arranged into two layers: an inner circular layer and an outer longitudinal one. The rectal muscularis of both studied species is thicker than that of the rest of the intestine.

The present investigation aims to illustrate the morphological and ecological differences of tortoises and terrapins. Two types of chelonian reptiles were selected; the herbivorous land tortoise, Testudo graeca terrestris and the freshwater terrapin, Pseudemys scripta elegans. Testuda graeca terrestris is highly adapted to live on land since it can live for a long period without water on sand dunes and semidesert areas during warm days. It is characterized with a dome shell and stumpy legs. All tortoises are vegetarians that fed on lettuce. On the other hand, the freshwater terrapin; Pseudemys scripta elegans is known to inhabit the Mississippi valley. It is semiaquatic reptile, known as red eared terrapin, spends in fresh water as much time as it spends on land. Pseudemys scripta elegans may by kept as pet with few hazards as it may cause Salmonellasis. This species is omnivorous since they feed on fishes, frogs, flesh, snails, worms and numerous aquatic plant species.