THE INTESTINAL PROTOZOA OF FROGS AND TOADS, 251 
Their size is variable; they measure from ca. 10 « to 16 win 
diameter—on the average 12-13. The diameter of the 
nucleus 1s ca. 6 yp. 
The cysts remain in this uninucleate condition for some 
time—exactly how long I have not been able to determine. 
Then the nucleus begins to divide. In the living animal it is 
seen to grow out into a long spindle, which subsequently gives 
rise to the two daughter-nuclei, but no details can be seen. 
In stained preparations, however, the whole process of divi- 
sion can be followed out in every stage with extraordinary 
clearness (see figs. 65-70). The first thing observable is 
the formation of two httle outgrowths at opposite poles of 
the nucleus (fig. 65). As these gradually draw apart the 
nucleus assumes the characteristic and remarkable spindle- 
figure (fig. 66). The karyosome lies at first in the middle of 
the spindle (fig. 65), but subsequently its component granules 
dispose themselves on the longitudinally arranged spindle 
fibres, as shown in fig, 67. At this stage the spindle extends 
almost from one side of the cyst to the other. Subsequent 
differentiation into two daughter-nuclei takes place through 
the rearrangement of the karyosomic granules to form two 
daughter-karyosomes, and through the subsequent constric- 
tion of the middle of the spindle (figs. 68, 69). When this 
is finally completed two daughter-nuclei, exactly like the 
original nucleus except that they are smaller, are seen inside 
the cyst (fig. 70). 
In this binucleate condition the cyst remains for but a short 
time. ‘hen both nuclei divide. They do not divide in quite 
the same way as the original nucleus. Instead of forming a 
spindle by outgrowth at opposite poles, as originally happened 
(fig. 65), they each form a spindle by outgrowth at one pole 
only (cf. figs. 71, 72, 73).1_ The karyosome therefore lies at 
' Tt might be thought that these two nuclei (fig. 71) are not about to 
form the second spindles, but are just finishing the first division—the 
drawn-out poles being the points which were connected, as in the right- 
hand pair of nuclei in fig. 74. Many considerations render such an 
interpretation highly improbable. In the first place, in the living 
