226 Papers from the Marine Biological Laboratory at Tortugas. 



to protrude beyond the original boundary of the cell, causing the spermato- 

 some to acquire a flask-shaped appearance (figs. 3 and 46). In the "neck" 

 of the spermatosome, those yolk bodies which were the first to be formed 

 come to lie between the broad surfaces of the bundle of axial fibers and the 

 cell-membrane; the edges of the bundle, on the other hand, lie in close 

 contact with the cell-membrane (figs. 3, 4, and 48). 



At this stage, in the living spermatosome, there is always to be seen a 

 very noticeable protuberance on one side of the brush formed by the flagella. 

 This structure, although it is only a transitory one, is very constant in the 

 living cells. The first indication of it is shown in figure 2, where it appears 

 as a swelling at the base of the cell. Later it becomes very much longer 

 and flattened in one axis (figs. 3 and 4) and appears finally to be withdrawn 

 into the cell-body (fig. 5). The only trace of this protuberance that could 

 be found in sectioned material is shown in figure 40. The point at which 

 this protuberance occurs must mark the weakest part of the cell membrane; 

 this is shown by the changes that occur when degeneration sets in. After a 

 spermatosome in the stage represented by figures 3 or 4 has been in an 

 artificial medium for two or three hours, the protuberance begins to become 

 very much distended. This is followed by a shifting, to that quarter, of 

 all the free contents of the cell, with the result that the bundle of axial 

 fibers, instead of passing through the cytoplasmic body, lies tangentially 

 to it and is surrounded by the cell membrane alone. This protuberance 

 may be interpreted as a precocious lengthening of the cell in a posterior 

 direction, the completion of which is prevented by the actual attachment 

 of the fibers to the cell-wall. As will be shown presently, such a lengthening 

 does take place at a very much later stage, but this time it is accomplished 

 through the direct agency of the axial fibers themselves. 



After a spermatosome has reached the stage represented by figure 46, 

 a longitudinal split occurs in the bundle of axial fibers, dividing it into two 

 approximately equal halves (fig. 47). This is caused by the continued 

 growth of the axial fibers without a corresponding lengthening of the cell. 

 Growth of the spermatosome does take place, to be sure, resulting in its 

 becoming longer and narrower, but this growth is not commensurate with 

 that of the axial fibers, nor is it accompanied by an increase in the volume 

 of the cell. If these facts are borne in mind, then the following steps in the 

 formation of the undulating membranes will be easily understood. 



After the split occurs in the bundle of axial fibers, the two halves, or 

 the secondary bundles, as they may now be called, move apart from each 

 other, and gradually approach the cell-membrane from opposite sides. 

 A lateral view of one of the secondary bundles, shortly after this movement 

 has commenced, is shown in figure 48. By comparing figures 47 and 48, 

 it will be seen that the albuminous bodies already formed are so placed that 

 they do not obstruct the path of the fibers ; those that eventually come to 

 lie in the middle and posterior portion of the spermatosome are not secreted 

 until after the fibers have reached the membrane on each side of the cell 



