Ultrastructure of spermatogonia and primary spermatocytes of C57BL6J mice

The three types of spermatogonia were confirmed. Type A spermatogonia have a large nucleus and loose chromatin and are poor in endoplasmic reticulum. The second type, B spermatogonia, have rounded and smaller nuclei filled with more electron-dense nucleoplasmic material. The endoplasmic reticulum has the aspect of round or elongated cisterns that are free in the cytoplasm or close to the basement membrane. In contrast, intermediate spermatogonia present chromatin material with intermediate condensation compared with the two previous cell types. Primary spermatocytes are characterized by the presence of intercellular bridges and a synaptonemal complex. In the late pachytene stages, the synaptonemal complex was found to be enveloped by chromatin material.

Morphological studies on the heart ventricle of African catfish (Clarias gariepinus)

The histological and ultrastructural characteristics of the heart ventricle in Clarias gariepinus (African catfish) has been studied by light microscopy and transmission electron microscopy. The ventricle of the heart has a saccular shape and the myocardial wall consists of an outer thin compact myocardium and an inner well-developed spongy myocardium. The myocardial layer has small myocytes, interstitial spaces and blood vessels. The myocytes are the major constituents of the ventricular wall. They are long cells, with large nuclei, and predominantly euchromatin. The sarcoplasmic reticulum of the ventricular myocytes consists of a network of tubules and subsarcolemmal cisternae oriented mainly along the longitudinal axis of the myofibrils. In contrast to the ventricular structure of other fish species described in the literature (Greer-Walker et al., 1985 Santer, 1985 Sanchez-Quintana et al., 1995, 1996), the African catfish, a freshwater sedentary fish recently introduced in neotropical climatic environments, showed a saccular ventricle that consisted of two muscle layers, a thin compact layer with large vessels and a developed spongy layer. The ultrastructure of the ventricular myocardium of C.gariepinus is similar to that of other teleosts, inclusive that of fish with other swimming habits.

Anatomical study of the diaphragm of the opossum (Didelphis albiventris)

The anatomical characteristics of the South American opossum diaphragm were described. Five male and seven female adult opossums, weighing between 700 and 1110 g, were used. Animals were killed by ether inhalation saturation. The abdominal and thoracic walls were dissected and opened, the viscerae were removed and the diaphragm anatomy was described and photographed in situ . After diaphragm removal, some dimensional data were taken and tabled. Primary branches of the phrenic nerves were dissected under a surgical microscope. The secondary branches were studied and described by transillumination after clarification in acetic acid. The opossum diaphragm is domed and has a mean area of 54.33 +/- 3.8 cm(2) . Well-identified costal, sternal and lumbar parts form the peripheral muscular region. The central tendinous region presents with a V-like form. Three folioles comprise the phrenic centre and present different dimensions. The caudal vena cava passes through its foramen between the ventral and right dorsal folioles. Both right and left phrenic nerves present one ventral branch and one dorsolateral trunk in 50.0% and 66.67% of the cases, respectively.