The Spermatogenesis of the Opossum (Didelpliys virginiana) etc. 85 
Fig. 58. Early stage of spermatid showing 8 chromosomes (postmeiotic stage). 
Fig. 59. Early postmeiotic stage showing 9 chromosomes. 
Figs. 60 and 61. Early stages in the process of metamorphosis of spermatid 
into Spermatozoon. Chondriosomes (mitochondria) abundantly present ; a small number 
appear to be formed anew in the early spermatid stage. 
Fig. 62. Later stage in metamorphosis showing Separation of homogeneous 
idiozome (centrosphere) from the hyaline Nebenkern (“sphäre”; remains of achromatic 
spindle?). 
Figs. 63 and 64. Still later stages illustrating the migration of the idiozome and 
the indentation and overflow of the nucleus hy the Nebenkem. A large plasmosome 
appears in the nuclei of tliese early stages. 
Fig. 65. Similar stage illustrating the cytoplasmic contents of deep staining 
peripheral granules and large mossv bodies (chondriosomes) and minute spherical va- 
cuoles (dissolving chondriosomes?). 
Fig. 66. Later stage showing the idiozome at opposite pole from the Nebenkem 
which has begun to flow backward around the nucleus. 
Fig. 67. Still later stages showing mainly the elongation of the nucleus and 
its migration to the surface of the cell. Two small chromatic granules (centrosomes ; 
centrioles) lie close to the idiozome and have probably originated from it. 
Figs. 68, 69 and 70. Successively later stages showing the characteristic shape 
and position of the Nebenkem (anterior remnant), nucleus (with liglitly-staining reti- 
culum), plasmosome, idiozome and diplosome (centrosomes). At this stage the Ducleus 
dips down at its peripheral end and takes a final position at the surface at right angles 
to its forrner position in the long axis of the elongated cell. 
Fig. 71. View of longitudinal section of nucleus after migration. The nucleus 
has become more compact and uniformly chromatic. To its inner surface are attached 
the centrosomes from one of which the tail filament grows. The cytoplasm surrounding 
the filament, and from which the future body and flagellum develop, represents only 
a portion of the original body of the spermatid. Irrespective of the nucleus (which 
is migrating) this illustration represents a sagittal section of Fig. 72. The space of 
the oval contains the Nebenkern which has spread over the head. 
Figs. 72 and 73. Side and surface views respectively of the nucleus (head) of 
this stage enclosed by enveloping Nebenkern. 
Figs. 74, 75 and 76. Three successively later stages in the process of transforma- 
tion of nucleus of spermatid to form head of Spermatozoon. 
Fig. 77. Side view of spermatid at stage when the Nebenkern has completely 
enveloped the compact chromatic head, and has delimited the portion of the cytoplasm 
which is to contribute the mitochondria for the spiral filament. 
Fig. 78. Side view of spermatid at slightly later stage. The head has become 
broader in front preparatory to Splitting. The portion of the cytoplasm which will 
contribute to the body and middle-piece is outlined by the Nebenkern which completely 
envelops the head. This portion contains a spherical Nebenkem-remnant. The 
axial filament extends the length of the elongate spermatid. The latter contains the 
idiozome. Some of this cytoplasm, with the mitochondria, will contribute to the flagel- 
lum, while a considerable portion will be cast off. 
Figs. 79 and 80. Later stages showing the U-shaped chromatic head, and the 
centrosome from which the axial filament grows out into the elongating body and tail. 
