SEA-FISHERIES LABORATORY. 453 
ripen the alveoli become filled with the products, and 
thus there is a general expansion of the reproductive 
mass, and the alveoli near the surface appear to the naked 
eye as rounded elevations or as small eggs. 
In teased preparations of the ripe ovary the alveolt 
are so numerous that it is difficult to see the connecting 
tubules, but in sections they are easily traced by their 
ciliated lining, and may be seen gradually joining up to 
form the reproductive ducts. These ducts can only be 
definitely traced by serial sections, but in some specimens 
of P. maximus the duct on the right side, which is by far 
the largest, can be seen with the naked eye as a thick 
white thread running parallel with, and very close to, 
the junction of visceral mass and renal organ until it 
opens into the latter. Ifthe point of an injecting syringe 
is inserted near the opening, this duct may sometimes be 
injected, but unless it is visible through beimg near the 
surface, care must be taken not to mistake an injected 
arterial vessel for it. ‘The duct on the left side is much 
smaller and only extends a little way, acting as conduit 
for the male portion on the left side in the neighbourhood 
of its opening. ‘The rest of the gonad is supplied by 
branches of the large duct which opens on the right. 
The main ducts are lined by an epithelial layer of 
columnar ciliated cells (fig. 54, Go.d.), the height of 
which is about twice the diameter, while the cilia are 
about as long as the cells. This epithelial layer is 
supported by somewhat delicate connective tissue which 
is continuous with the scattered strands that cross in all 
directions and pass round the alveoli and the ducts, 
forming a framework for the reproductive organs. 
This columnar ciliated epithelium passes into the 
flattened germinal epithelium (fig. 53, Ge. ep.) lining the 
alveoli, and in the ovarian region ova in various stages 
