Papers from the Marine Biological Laboratory at Tortugas. 239 



36 and 39. Sections through two spermatosomes showing consecutive stages in the growth 



of the axial fibers. 



37 and 38. Two consecutive sections through the bundle of axial fibers of a spermatosome 



in a stage corresponding to that shown in figure 39. Note the almost round base 

 and the flattened anterior portion of the bundle and the mitochondrial apparatus 

 surrounding the latter. 

 40 and 41. Sections through two spermatosomes of approximately the same age; the sec- 

 tions pass in planes which are at right angles to each other. Figure 41 gives a 

 surface view of the bundle of axial fibers and the mitochondria surrounding it; 

 note the increase in the size of the chromatic vesicles shown here. 



42. A cross-section through the posterior region of a spermatosome which is a little older 



than the preceding ones. Note how closely the mitochondria are applied to the 

 bundle of axial fibers. 



Plate 5. 



(Initial magnification 3450 diameters, reduced one-third.) 



43. A section through a spermatosome showing the further growth of the bundle of axial 



fibers. 

 44 and 45. Sections through two spermatosomes showing the bundle of axial fibers extending 



across the cell and the early formation of the secreted bodies; the sections pass 



in planes which are at right angles to each other. 

 46. A section through a spermatosome showing the continued growth of the bundle of 



axial fibers until it extends beyond the cell. 

 47 and 48. Sections through two spermatosomes of slightly different ages showing the 



splitting of the bundle of axial fibers; the sections pass in planes which are at right 



angles to each other. 



Plate 6. 



(Initial magnification 3450 diameters, reduced one-third.) 

 49. A longitudinal section through a spermatosome in a well-advanced stage. The splitting 

 of the bundle of axial fibers has been completed and the cell is partially filled with 

 the secreted bodies. The nuclear vesicles are rapidly degenerating. 

 50 to 58. Consecutive cross-sections through a single spermatosome a little younger than 

 that shown in figure 49. The sections are taken in order from the posterior to 

 the anterior end of the spermatosome and show the modifications of the two 

 halves of the bundle of axial fibers as they reach the cell-wall on each side. 

 59 and 60. Cross-sections through the posterior and anterior halves of two spermatosomes 

 of the same age showing some of the axial fibers moving out beneath the cell-wall. 



Plate 7. 



(Initial magnification 2450 diameters, reduced one-third.) 



63. A longitudinal section through a spermatosome in which the halves of the bundle of 



axial fibers have reached the cell-wall on both sides throughout their entire length. 

 The secretion of the albuminous bodies has not yet been completed nor has all the 

 chromatin disappeared. 



64. A longitudinal section through a nearly adult apyrene spermatozoon showing the total 



disappearance of the chromatin and the cell filled with the secreted bodies. 



65. A longitudinal section through an apyrene spermatozoon of the same age as that shown 



in figure 64 giving a surface view of one of the two undulating membranes and the 

 longitudinal fibers beneath the cell-wall. 



