GERM CELLS OF ANURANS 255 
Following the pachytene is the period of exconjugation or dis- 
junction of the homologous chromosomes, i.e., the longitudinal 
spHtting of the thick double threads into two thin threads which 
diverge in the center, but remain united at both ends (figs. 14, 
15, and 40 to 51). This stage corresponds to the diplotene of 
Winiwarter ('00) or the prostrepsinema of Janssen ('05). The 
pachytene threads split longitudinally, the split first appearing 
apparently at the distal pole of the nucleus and extending prox- 
imally. The line of cleavage might possibly be looked upon as 
marking the earlier line of fusion of the two originally unpaired 
leptotene threads, and hence be regarded as the line of disjunc- 
tion (figs. 14 and 15, also 40 to 51). This is only guesswork, 
however, because in general the fused leptotene threads show no 
sign of .separation in the pachytene as they do in other forms; 
i.e., the primary longitudinal split is usually invisible at this 
stage. 
The diplotene stage in Rana catesbeiana larvae is marked by 
extreme growth of the cell, especially the nucleus which reaches 
gigantic proportions in many instances. In general the cells of 
the pachytene stage, though larger than those of the leptotene, 
do not present such marked size differences over leptotene stages 
as do the diplotene nuclei over both pachytene and leptotene. 
In early diplotene, when the primary longitudinal split is just 
making its appearance, there is somewhat superficial resemblance 
to the amphitene stage. The similarity is, however, slight, and 
one could hardly confuse the two periods. The longitudinal spht 
of the diplotene appears first at what corresponds to the distal 
pole of the double thread. In the amphitene just the reverse 
condition is presented, the initial pairing of the leptotene filaments 
begins first at the proximal pole. The very obvious difference 
in the size of the nuclei of the two periods is an excellent criterion 
for distinguishing the two stages. Also separation is never com- 
plete in the diplotene, as the homologues remain united at their 
ends ; conversely, in the amphitene the unpaired leptotene threads 
at the distal pole of the nucleus diverge widely from one another. 
Shortly after the process of disjunction, a secondary longitudi- 
nal splitting of each member of the pair appears, forming the 
