The relations between neural and intermediate lobes in the pituitary of Squalus acanthias.

Abstract

1. The neural and intermediate lobes of Squalus are separated by a connective tissue membrane, which is absent in only few places. 2. The neural lobe consists of three layers: ependymal, fibre and external layer. The ependymal layer contains two cell types, ependymal cells and secretory cells (Sterzi). The fibre layer is mainly formed by neurosecretory nerves, which end within the lobe. The external layer consists of a stroma of branched ependymel fibres, and neurosecretory material. 3. Along the membrane between the two lobes is a capillary network, the neural lobe plexus. 4. The intermediate lobe consists of irregular cell columns and large blood sinuses. The cell columns have a zone of strongly staining cytoplasm nearest the vessels. 5. Inside the cell columns is a system of intra-columnar connective tissue and intra-columnar arteries, the latter ending in the neural lobe plexus. 6. Nerves from the neural lobe sometimes enter the intermediate lobe, either directly through the membrane, or at places where the membrane is absent. The nerves may run between the intermedia cells or in the intra-columnar connective tissue. 7. The intermediate lobe of Squalus is penetrated by nerves only to a slight degree, in contrast to other Elasmobranch species (Scyllium, Mustelus, Pristiurus, Raja, Dasyatis, Torpedo). 8. A comparison is made between different types of Elasmobranch neurointermediate lobes, and with the neurohypophysis of other Vertebrates. It is found that Squalus has a neural lobe of fairly primitive structure, while its intermediate lobe reaches a high degree of specialization.