Abstract
The external and histological features of pituitary gland of sea-lamprey, Lampetra (=Entosphenus) japonica (MARTENS), are described. The specimens were collected from the Ohkozu river, a branch watercourse of the River Shinano in Niigata Prefecture, at the time of ascending the river with the approach of its breeding season.
1. The pituitary components of L. japonica consist of four parts, which are similar to those of higher vertebrates ; they are subdivided into three glandular (or adenohypophysial) parts and a neural one. Thus, the following nomenclature would be applicable to these constitutional components: (1) pro-adenohypophysis, (2) mesoadenohypophysis, (3) meta-adenohypophysis and (4) neurohypophysis.
In general three parts of adenohypophysis are separated respectively with the septa of connective tissue, there is a streak capillary between meta-adenohypophysis and neurohypophysis.
2. Pro-adenohypophysis is mainly composed of the masses of cyanophilic and acidophilic cells which are disposed in vertical rows. Though this part has been named anterior lobe or medullary core of pars distalis, it seems to be homologous to pars principalis of pars anterior in higher vertebrates.
3. Meso-adenohypophysis is composed of predominant acidophilic cells which are also disposed in vertical rows. This part has been named Ubergangsteil or cortical zone of pars distalis, however a part of this is presumed to be homologous to pars tuberalis of pars anterior in higher vertebrates.
4. Meta-adenohypophysis is mainly constructed from high columnar acidophiles which are disposed in a band or a cord, and is unique part which keeps touch with neurohypophysis. Though the previous investigators called this part intermediate lobe or pars infundiburalis, this seems to be homologous to pars intermedia of higher animals.
5. Neurohypophysis is merely an expanded part of ventral wall or floor of recessus infundibuli, and consists of two parts, which are the cellular part originated from the ependyma of brain at the dorsal region and the neuroglial part at the ventral region.
