Eye
Skin
This is a skin sample from the ventral aspect of the pectoral fin or wing. The layers include the epidermis (stratified squamous epithelium), multicellular epidermal glands, and the dermis comprised of loose connective tissue and dense collagen. Melanocytes or chromatophores are deep to the dermis. Other tissue deep to the dermis is shown in the slide under Ampullae of Lorenzini.
Ampullae of Lorenzini
The ampullae of Lorenzini are specialized electrosensory receptors located in the skin on the head and wings. Their use includes detecting changes in electric fields as a result of nearby prey and for navigation and orientation (Bleckmann and Hofmann, 1999). The images below show cross sections of the ampullary canals in the skin. The ampullary canal walls and inside consist of squamous epithelium (resistance of 6 million ohms/cm) and mucopolysaccharides (20-25 ohms/cm, similar to seawater), respectively (Bleckmann and Hofmann, 1999).
Brain - Telencephalon
Brain - Cerebellum
Brain - Optic Nerve
Esophagus
Organ of Leydig
The organ of Leydig is a lymphomyeloid tissue embedded within the submucoa of the esophagus. In some species of elasmobranchs, a similar Leydig organ is found in the parenchyma of the testes and ovaries, known as an epigonal organ in this species (Zapata et al., 1996). The organ of Leydig in the esophagus is lobed and contains large amounts of granulocytes, lymphocytes, and plasma cells.
Pancreas
The pancreas is located in the curve of the proximal intestine and has both exocrine and endocrine portions. The sparse ducts (right) within the exocrine pancreas deliver enzymes that are released into the intestine during digestive activity (Holmgren and Nilsson, 1999). The endocrine cells occur amongst the vast exocrine pancreas as small islets.
Spleen
The spleen is similar in appearance to mammalian spleen and located within the lesser curvature of the stomach. It consists of red and white pulp. The white pulp can consist of lymphocytes, monocytes, macrophages, and some granulocytes and plasma cells. The red pulp can be seen between the white pulp and consists of erythroid tissue (Satchell, 1999).
Liver
Epigonal Organ
The epigonal organ consists of hematopoietic tissue similar to bone marrow in mammals. It is located dorsally and primarily along the left side of the coelomic cavity, although it may extend caudally and around to the right side. The outer margin on the left side is closely associated with the ovary where multiple stages of follicular development are seen (left image). Cords of granulocytes interspersed with sinuses of erythrocytes are seen at higher power (right image).
Ovary
The ovary is located on the left side in the coelomic cavity and attached or associated with the margin of the epigonal organ. The image on the left shows a cross section of a vitellogenic follicle. The folds within the follicle are the follicular wall made up of large and small follicle cells lined with the zona pellucida surrounding the ovum (Hamlett et al., 1999). The image on the right shows two follicles. The follicles are located within a connective tissue matrix (tunica albuginea) beneath the germinal epithelium (crossing the bottom right corner of the image) and along the margin of the epigonal organ (not shown). The outer, single-cell layer is the follicular wall which surrounds the zona pellucida of the follicle.
Uterus
The uterus shown here has early-term trophonemata. Trophonemata form on the mucosal surface of the uterus. They are villous, spatulated, finger-like projections that serve to secrete histotroph of uterine milk to the fetuses (Hamlett et al., 2005). Simple cuboidal epithelium line the surface of the trophonemata. Glandular cells with granules are also seen with secretory product or lipid deposits.
Oviducal Gland
The oviducal gland is between the oviduct and uterus. In viviparous species this gland serves to envelope the ovulated egg in egg jelly and a capsule (Hamlett and Koob, 1999). The interior of the oviducal gland is lined with an epithelium of simple columnar secretory cells forming thick longitudinal folds (Henderson et al., 2014). The zone shown here is likely the baffle region (Hamlett et al., 1998).
Kidney
Rectal Gland
The rectal gland is multilobulated structure attached to the distal end of the spiral intestine. Each lobe has a central duct surrounded by layers of acini (secretory parenchyma) contained within the outer capsule (upper right corner of left image) (Olson, 1999). The central duct (off the left side of the left and right images) has a mucosal lining of pseudostratified epithelium (similar to the colon). The acini surrounding the duct contain a proteinaceous product.