[•21 



ripen the alveoli become filled with tlie products, and 

 thits 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 alveoli 

 are so numerous that it is difficult to see the connecting 

 tubules, but in sections they are easily traced by theii' 

 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, -.vhich 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. If the point of an injecting syringe 

 is inserted near the opening, this duct may sometimes be 

 injected, but unless it is visible through being 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 



