SECRETING STRUCTURES. 421 



extremities. In others the cylindrical elongation has taken 

 place in all the included cells, with the exception of a lew, 

 which still retain the rounded form, at a spot opposite to that 

 part of the vesicle in which the cliange commenced ; and at 

 the same time it may be observed, that tlie cylindrical cells 

 have become arranged in a spiral direction within the parent 

 vesicle. Lastli/, Vesicles exist in which all the cells are 

 cylindrical, and are arranged within its cavity in a spiral- 

 direction. 



The changes which occur in the included nucleated cells 

 of the vesicle are highly interesting. After the nucleus of 

 each has become developed into a mass of cells, the parent 

 cell becomes, as has been stated, cylindrical. The change in 

 the shape of the cell is contemporaneous with the appearance 

 of a spiral arrangement of the included mass of cells. This 

 spiral arrangement is also contemporaneous with an elonga- 

 tion of each cell in the mass, in the direction of the axis of 

 the parent cell. When the elongation has reached its maxi- 

 mum, the original mass of included cells has assumed the 

 appearance of a bunch of spirals, like corkscrews arranged 

 one with another, spiral to spiral. In particular lights the 

 cylindrical cell presents alternate spots of light and shade, 

 but by management of the illumination, the included spiral 

 filaments become evident ; the light and shade are seen to 

 arise from the alternate convexities and concavities of the 

 spiral filaments, combined in a spiral bundle. 



In vesicles more advanced, the wall of the cylindrical cells 

 has become attenuated. 



In other vesicles the diaphragms across their necks have 

 dissolved or burst, the bundles of spiral filaments float along 

 the ducts of the gland, or separate into individual spiral fila- 

 ments. These filaments are completely developed spermatozoa, 

 pointed and filamentous at both extremities, thicker and 

 spiral in the middle. 



