EXPLANATION OF PLATES 
All of the figures were drawn from material fixecl in Flemming and stained in 
iron haematoxylin; sections in most cases were 5^ in thickness. All were drawn 
with the aid of a camera lucida, using 1.5-mm. Zeiss apochromatic objective 
and no. 12 ocular, with 160-mm. tube length. Drawings w^ere made at table 
level and are reproduced without reduction in size. 
PLATE 1 
EXPLANATION OF FIGURES 
Figures 1 to 13, Asilus sericeus. Figures 1 to 5, spermatogonia. Figures 6 
to 13, telophases of final spermatogonia and early growth stages of first sper- 
matocyte. 
1 Late resting stage or early prophase, the chromatin aggregated into five 
bodies that represent the five pairs of chromosomes. 
2 Two prophases, nuclei entire, each showing the five pairs of chromosomes, 
resembling bivalents. Note the differences in degree of condensation of the 
different elements. 
3 and 4 Early and late metaphases. 
5 Final spermatogonial anaphase, showing the paired association of the 
chromosomes as they go to the poles; nucleus is cut so that one pair is missing 
from the lower pole. 
6 Late anaphase or early telophase of the final spermatogonial division. 
The nuclei are practically entire and the chromosomes are all represented. The 
figure at the right is slightly earlier than the one at the left, but the union of 
the chromosomes in pairs is so intimate that only one shows the dual structure. 
In the figure at the left the duality is scarcely visible, and not more than the 
haploid number of chromosomes can be detected; the two lying side by side at 
the lower pole are separate pairs, not members of one pair. 
7 Approximately the same stage as 6. The union is progressively more inti- 
mate from the lower to the higher of the three nuclei. The nuclei are practically 
entire and each shows four or five bivalent chromosomes. 
8 An entire nucleus of the same stage, showing the five bivalent chromosomes; 
scarcely any trace of duality is revealed. 
9 Four cells in late telophase after the nuclear membrane has appeared and 
the chromosomes have moved apart and lost much of their staining capacity. 
Only part of the chromatin is represented. 
10 Stage a, slightly later than the preceding; the chromosome remains are 
barely visible; nuclei not entire. 
11 to 13 Stage h, the chromosomes again taking the stain and reappearing 
in the form of five long bivalents, one of which forms part of the large nucleolus; 
nuclei entire. 
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