476 JEAN REDMAN OLIVER 



body (figs. 13 to 15) toward the tubule wall. The prolongation, 

 described by Duesberg ('08) in the spermatid of the rat, which 

 the nucleus sends out to meet the centrosomes is not visible in 

 the fur seal. In the second period the nucleus is often elongated 

 in such a manner, but it is long after the centrosomes have 

 reached the nuclear membrane. 



The idiosome, or sphere, of the fur seal shows in most respects 

 those characteristics which have been described by previous 

 authors in mammalian spermiogenesis. It appears shortly after 

 the second division of the spermatocytes as a homogeneous body 

 of considerable size, lying close to the nuclear wall, and usually 

 near its proximal end. It takes an eosin stain a little more 

 deeply than the surrounding cytoplasm, and shows no traces of 

 the cortical granulations or other structural differentiations de- 

 scribed for some forms. In shape it is not strictly a sphere but 

 has more the form of a prolate ellipsoid (fig. 1, s). The testis 

 of the fur seal is not as favorable material for the study of the 

 development of the acrosome as that of some other forms, but 

 the course of events can be readily followed, and differs but 

 slightly from that described by Benda ('91), Moore ('94), Niessing 

 ('96), Lenhossek ('98), Meves ('99) and others. The first change 

 in the homogeneous idiosome that I have been able to find is 

 the relatively sudden appearance of two densely staining gran- 

 ules, lying in a clearer area within it (fig. 2). The whole sphere 

 stains very faintly at this stage and appears hyaline and semi- 

 transparent. These two granules apparently fuse into a single 

 dense body in the center of the hyaline area (fig. 3). Not all of 

 the sphere is made up of this hyaline substance, however, a 

 denser and more opaque portion lying at one side (fig. 4, s.r.) 

 and gradually separating entirely from the clear portion, destined 

 to form the 'capuchon,' or head cap of the mature spermatozoon. 

 This darker remnant of the sphere migrates to the distal part 

 of the cell (figs. 13 to 15) where it finally degenerates along with 

 the cytoplasm of that region, and is cast off in the closing stages. 

 The hyaline body is at first sphe;rical (figs. 3 and 4) but soon 

 begins to flatten against the nuclear wall, its contained central 

 granule, the acrosome, coming in contact with the latter and 



