228 Papers from the Marine Biological Laboratory at Tortugas. 



one direction and then in the other; it is simply an accompaniment of the 

 separation of the secondary bundles and after these have reached the cell- 

 membrane such twists as have taken place are apparently undone. At all 

 events, as the secondary bundles begin to push out beyond the cell-body, a 

 rearrangement of the inner fibers occurs in that they form a number of 

 horizontal layers (figs. 56, 57, 58, and 60). Some of the inner fibers, appar- 

 ently, crowd into the layer of exterior ones, taking the place of those that 

 have moved away, while the others continue to form a decreasing number of 

 horizontal layers. The result is that the bundles become wider and flatter. 

 This is shown in cross-section in figures 61 and 62 and in surface view in 

 figure 65. The first of these figures is an oblique section through the anterior 

 region of a spermatosome at about the stage represented by figure 64. The 

 section represents a cross-section just behind the centrosomal plate of 

 another spermatosome of the same age. Figure 65 is a longitudinal section 

 through a spermatosome which was almost identical with the one repre- 

 sented by figure 64. In this last figure the myoneme-like striations are 

 also shown in surface view. As is shown here, the same force (that is, the 

 continued growth of the axial fibers without a fully compensating increase 

 in the length of the cell-body) which causes the secondary bundles to reach 

 the surface of the cell and then to extend beyond it, eventually causes several 

 folds to occur throughout their length. This is also indicated in figure 61. 



After the secondary bundles have reached the cell-membrane, the space 

 which has been vacated by them is filled with a substance whose consistency 

 is greater than that of the cytoplasm surrounding the albuminous bodies 

 (fig- 53)- Indeed, there seems to be a general flowing of the denser, more 

 granular ctyoplasm to the center of the cell, leaving the homogeneous 

 enchylema to fill the spaces between the albuminous bodies (figs. 59 and 60). 

 Eventually this denser part of the cytoplasm becomes differentiated in such 

 a way that it forms a fibrillar core passing down through the center of the 

 cell (fig. 64). 



The changes in the shape of the spermatosome, as a result of the splitting 

 of the bundle of axial fibers and the subsequent growth of these fibers 

 themselves, are shown in figures 47, 49, 63, and 64. At first, accompanying 

 the spreading of the secondary bundles to the surface of the cell, there is a 

 slight elongation of the spermatosome in an anterior direction (fig. 49). 

 This is continued until the secondary bundles begin to protrude beyond 

 the cell-body, when it practically ceases (fig. 63). It will be noticed that 

 the centrosomal plate has been pushed right up to the very anterior tip of 

 the spermatosome. The further growth of the fibers results next in the 

 lateral extension of the secondary bundles beyond the cell-body throughout 

 their entire length and then in the elongation of the spermatosome in a 

 posterior direction (fig. 64). This fact is evidenced not only by the change 

 in the contour of the posterior end of the spermatosome, but also by the 

 redistribution of the mitochondria. The base of the cell has become pointed 

 and the flagella have fused to form the extreme end of the tail-piece. About 



