360 The Spermatogenesis of Bufo Lentiginosus 
typic type, and forms like Gryllotalpa and Bufo in which rings give 
place to tetrad groups before the metaphase and division is reductional. 
Where tetrads are formed in the prophases of the first maturation 
mitosis it is, of course, not possible to determine whether the first or the 
second division is reductional. As the first maturation division of the 
chromosomes that have the shape of dumbbells and also of those that 
take the form of rectangular blocks is transverse, it seems safe to assume 
that the tetrads are so placed on the spindle that univalent chromosomes 
are separated in the first mitosis. 
The formation of the first maturation spindle evidently takes place 
very quickly, as I have been able to find only a comparatively few stages 
in its development. Soon after the synizesis stage the centrosome divides 
and the attraction-sphere disappears as it does before the formation of 
the spindle in the spermatogonial mitoses. As the centrosomes move 
apart, each becomes the centre of a very small aster formed, presum- 
ably, of the substance of the attraction-sphere (Figs. 36, 41). As a rule, 
the centrosomes le at this time very close to the nuclear membrane 
which is somewhat irregular in outline. After the disappearance of the 
nuclear membrane, a small spindle is found with’ the centrosomes, sur- 
rounded by small asters, at the spindle poles (Fig. 42). The spindle 
grows rapidly, probably at the expense of nuclear material, and when 
fully formed in very large proportion to the size of the cell (Figs. 44- 
53). After the stage of Fig. 42 every trace of the polar radiation dis- 
appears and the centrosomes are totally devoid of any radiation in all 
subsequent stages. 
During, or soon after the synizesis stage, the acroblast becomes dumb- 
bell shape (Fig. 22, 4) and then constricts into two rounded bodies 
(Fig. 26). This division takes place before the centrosome divides, for, 
as shown in Fig. 26, one can occasionally find a section of a cell contain- 
ing the centrosome surrounded by its granular attraction-sphere and two 
acroblasts. During the formation of the spindle the acroblasts usually 
separate and in the metaphase are to be found some distance apart (Fig. 
48). Occasionally, as in the spermatogonial divisions, the acroblasts le 
close together in the equatorial region of the spindle and appear as very 
small chromosomes (Fig. 45, 4). During the anaphase the acroblasts 
have apparently no definite position in the cell as they may be found 
on the spindle, near to it, or close against the cell wall (Figs. 50, 53). 
They are, however, at this time always on opposite sides of the equator 
of the spindle, and when cell division takes place one acroblast goes to 
each of the daughter-cells. 
