256 WILBUR WILLIS SWINGLE 
tetrad-complex, made up of fom- chromatids (McClung, '00) 
united at the ends. This secondary split marks the line of 
separation of the chromatids in the subsequent equational or 
homotypic division, i.e., the second maturation division. In 
each chromosome this second split is apparently at right angles 
to the primary split. Coincident with the appearance of the 
secondary split is a process of shortening and thickening of the 
diffuse, thread-like tetrads. This shortening and condensation of 
the chromosomes marks the end of the diplotene (figs. 16 and 17). 
Following the stage just described, there occurs a series of 
transition stages leading up to the complete formation of the 
heterotypic tetrads on the mitotic figure. These stages are known 
by various names, but for present purposes Hacker's ('95) term 
'diakinesis' will be employed as including that period in the germ- 
cell cycle, from the first formation of the tetrads to their definitive 
arrangement upon the first maturation spindle. 
Diakinesis — formation of the tetrads 
The ring tetrads, so characteristic of the Amphibia, are formed 
by the disjunction of the homologous chromosomes that paired 
during the amphitene and pachytene and separated during the 
diplotene, except at their ends which remained in contact (figs. 
14, 16, 41 to 51). Thus, in the writer's opinion, the annular 
space represents, in Rana catesbeiana, the space between homolo- 
gous chromosomes. In other words the space between the rings 
represents the 'primary longitudinal split' and probably the orig- 
inal hne of fusion in parasynapsis of the autosome pairs. The 
first maturation division in the bullfrog larva is heterotypic or 
reductional for most of the tetrads in the sense that entire chromo- 
somes are separated. This conception has been held by various 
workers on urodele spermatogenesis. Thus Janssens holds this 
view for the urodele Batracoseps and the anuran Alytes and 
Montgomery for Plethodon cinereus and Desmognathus fuscus, 
though the latter writer arrived at this conclusion by assuming 
telosynapsis occurs first. He interpreted the pachytene loops 
correctly as bivalent chromosomes, but he misinterpreted the 
nature of the double spireme, in considering each loop as two 
