SPERMATOGENESIS OF EUSCHISTUS 769 
axis to take places to the right and left of this axis, carrying the 
remains of the idiozome with them. The earliest stage showing 
the centrioles is given in fig. 54, showing the centriole (c) upon the 
cell membrane; this cell contains still a trace of the sphere (Sp) 
but no remnant of the idiozome. Subsequently a pair of centrioles 
is found to the right and another pair to the left of the primary 
long axis (c, figs. 57-59). <A line joining these centriole poles 
is at right angles to the previous primary axis, as seen by com- 
paring figs. 57 and 58 with fig. 52. Each pair of centrioles lies 
in contact with the cell membrane, at the base of an indenta- 
tion; a line joining the two centrioles of a pair is usually oblique 
to the surface of the cell at that point. No flagella were found 
attached to the centrioles of the spermatocytes, not even in cells 
examined in life. 
As the pairs of centrioles come to occupy the positions described, 
two conspicuous movements of cell parts result, as one finds on 
examination of figs. 57-59, 61-63, 65, 66, 71, 84, 85. The first 
of these is that the original distinction between central and dis- 
tal poles becomes more or less obliterated in that the cytoplasm 
mass becomes almost as great at the former as at the latter pole, 
or in other words, the nucleus becomes more central. The second 
is that the nucleus becomes elongated in the direction of a line 
joining the centriole poles. Thus the nucleus assumes a marked 
ovoid outline, as seen best in figs. 59, 61, 63, 66, 71, 84, 85, with 
its ends pointed towards the centriole pairs. Therefore the cen- 
trioles exert a powerful attractive influence upon the nucleus, 
before any spindle fibers can be seen. 
The centriole pairs maintain their positions on the cell mem- 
brane until the stage of fig. 84, after which they sink into the 
cytoplasm. Fig. 85 shows one centriole pair still upon the sur- 
face, the other within a cytoplasmic knob, and fig. 86 shows both 
pairs close to the nucleus. Fig. 86 is interesting in showing a 
persisting primary axis, with the centrioles to the right and left 
13 In my previous studies centrioles were not found in these cells until the late 
prophases. 
44 Tn fig. 65, I could not be certain whether the centrioles lay upon the surface 
or beneath it. 
