42 
H. E. Jordan 
I. Points of Primary Interest. 
This investigation aims to trace the spermatogenctie history of the 
opossum. The points of special interest involved concern, a) the pre- 
sence of an unpaired idiochromosome (Wilson) or accessory cliromosome 
of McClung (heterotropic cliromosome, Montgomery = odd chromo- 
some or monosome (allosome) or chromatin — (cliromosome), nucleolus, 
Montgomery; or X-element, Wilson, of spermatogonia); b) the method 
of synapsis (telosynapsis) ; c) the presence of a hemioid group (resiüt of 
double numerical reduction) of chromosomes in the second maturation 
division; d) the origin and fate of chromidia (Hertwig 1902, Gol- 
schmxdt 1904): mitochondria (Benda, 1897) or cliondriosomes (Meves, 
1907); and e) the formation and morphology of the Spermatozoon. 
A discussion of the central facts in the spermatogenetic process will 
follow a preliminary complete record of events. 
II. Material and Methods. 
The material includes 4 pairs of festes ; 2 from young oppossum, 2 from 
large adults 1 )*). The younger testes contain, besides Sertoli cells (tropho- 
cytes), only spermatogonia and presynaptic spermatocytes. The adidt 
testes contain all the stages, with division figures and cliondriosomes in 
abundance. Material was fixed in Zenker’s fluid, Bouin’s fluid, corro- 
sive-acetic and in strong Flemming’s fluid. Only the last tliree fluids 
gave satisfactory preservation. The iron-haematoxylin method of stain- 
ing was used chiefly. Uncertainties of Interpretation (mainly differen- 
tiation between plasmosome and cliromosome nucleolus) were checked 
with sections stained with Auerbach’s methyl-green-acid-fuchsin solution. 
Delafield’s haematoxylin with eosin counterstain was also employed. 
Chondriosomes (cliromidia) were studied both in stained (iron-haema- 
toxylin) and unstained sections of FLEMMNG-fixed material 2 ). The study 
and illustrations were made by aid of 1 / 12 oil immersion lens. 
III. Spermatogonia. Diploid (duplex) Cliromosome Group. 
Only two generations of spermatogonia can be distinguished. The 
earlier generation (primary spermatogonia — seen more abundantly in 
the immature testes of the young individuals) appear similar, with re- 
spect to tlieir nuclear Organization, to the later generation (secondary 
spermatogonia — fig. 2). Both differ from the resting primary sperma- 
tocyte in that they have generally only one nucleolus (cliromatic). The 
*) See foot-notes pag. 76. 
