A comparative study of the pineal complex of nineteen species of Indian freshwater fishes.

The pineal organ of the teleosts investigated has a stalk of varying length which expands into a well defined end-vesicle (EV) of varied shape. In Heteropneustes fossilis the pineal stalk is so long that the EV is situated far in front of the anterior end of the brain. On the other hand the pineal of Amphipnous cuchia lacks a distinct stalk; as a result the EV is situated just above the subcommissural organ (SCO) within the dorsal limit of the brain. The pineal of Notopterus chitala is tubular in form, whereas that of A. cuchiya is compact and devoid of a lumen. In those fishes where the lumen is prominent, the EV is in open communication with the third ventricle through the hollow stalk. In between those species having tubular and compact EV there is a variety of form tending towards compactness apparently through the process of folding and proliferation of the epithelial cells. In the catfishes a definite pineal window is present. However, in N. chitala and Glossogobius giuris the roof of the cranium is thick over the pineal EV. But the scanty distribution of the pigment cells over the pineal apparently renders the area translucent. The dorsal sac (DS) and the pineal gland lacks a definite correlation in their structural relationship in the different species studied. In G. giuris and A. cuchia the DS is introverted into the third ventricle to form the choroid plexus and in many others it is in the form of an extroverted sac of varied size and shape.