GERM CELLS OF ANURANS 253 
Janssens ('01) first called attention to this condition in urodeles 
and considered it a definite stage of the germ-cell cycle. Later 
('05) he reversed his earlier opinion and stated the condition 
described earher was due to poor fixation. 
In the bullfrog larva there can be no question that S5nQizesis is 
an artifact due to poor penetration of fixatives. For instance, in 
well-preserved material it is impossible to find contraction stages; 
where large pieces of the gland are used, generally the peripheral 
portion of the tissue will show no synizesis, whereas the central 
portion will show numerous contraction figures. A comparative 
study of reagents, such as Bouin's or, better, Ezra Allen's modi- 
fication of Bouin's fluid without urea which is a good fixative for 
frog material, with Flemming's osmic fixative, a rather poor pene- 
trant, on similar sized pieces of gonad, gives illuminating results 
in regard to contraction stages. In Rana catesbeiana and Rana 
pipiens slow penetration of fixatives clumps the dehcate loops 
of the leptotene bouquet into a typical synizesis figure. 
The condition described here for anurans possibly is not com- 
parable to a somewhat similar clumping of nuclear contents in 
other forms described by various investigators. The writer has 
had the opportunity, through the courtesy of Dr. E. L. Shaffer, 
to examine synizesis stages in Cicada material. The conditions 
presented by this form are hardly comparable to those described 
here for anurans, and it ma}^ well be that in certain groups syni- 
zesis is a definite stage in the maturation cycle. 
The partial synapsis of leptotene threads in the amphitene is 
completed in the pachytene stage which immediately follows. 
The threads of this period are thickened throughout uniformly 
and usually show no trace of their dual nature, save perhaps in 
respect to size. It is odd that in a fully formed pachytene spi- 
reme there is usually no indication of the leptotene threads which 
entered into its formation (fig. 39, also 11). Most animals show 
distinct traces of a primary longitudinal split or line of fusion 
between the conjugants. For example, Wenrich ('16), describing 
the pachytene stage in Phrynotettix magnus, states: ''The fine 
of separation between the threads which have conjugated (i.e 
the primary longitudinal spUt) remains visible throughout the 
pacytene stage." 
