DEGENERATE (aPYRENE) SPERM-FORMATION OF MOTHS. 469 
fuse at all, or only a limited number fuse. These latter, as 
well as the isolated single chromosomes, endeavour to form 
new nuclei, and one gets the sort of cell drawn in PL 26, figs. 
1, 2, and 6. PI. 26, fig. 2, is quite typical. There were in the 
field seven abnormal nuclei, none of which had succeeded in 
forming a proper reticulum. In PI. 26, fig. 6, there were some 
five nuclei, the two bottom ones of which were normal in 
appearance. In PI. 26, fig. 1, the truth of these remarks is 
also illustrated ; some nuclei were apparently normal, though 
smaller; others were abnormal. Degeneration of the nucleus 
takes place at every stage of spermiogenesis. Even when the 
nucleus of the spermatid is apparently normally formed, it 
may in some other way show that it is not properly func- 
tional. PI. 26, figs. 3, 7, 8, 10, and 11, show degenerate 
stages in which the nucleus, though seemingly normal, fails 
to become attached to the centrosome, and drifts down the 
growing sperm. The centrosome keeps its position. In 
PI. 26, fig. 13, the several nuclei formed from the number of 
chromosomes which failed to join up all together have under- 
gone the usual staining change which takes place at this 
period, but only one nucleus has managed to keep its position 
at the head of the cell. In PI. 26, fig. 12, the very darkly 
staining nucleus has drifted down the sperm, and has 
attached to it a small acrosomic granule (6r.), which does not 
seem to be quite normal. In PI. 26, fig. 9, the nuclei are 
normally reconstituted, but, judged from the progress of the 
acrosome, are late in reaching this stage. All the nuclei in 
this nest were unable to keep their positions at the head of 
the cells. The section is somewhat oblique. 
With regard to the formation of the nuclei from single or 
fused chromosomes, every conceivable stage can be found, 
especially in Smerinthus and Pygaera, where failure to form a 
proper spermatid nucleus is common ; this also applies to 
Spilosoma, but in Pier is brassicae failure generally comes 
at the stage when the spermatid nucleus should adhere to the 
centrosome (PI. 26, figs. 10 and 11, etc.). PL 26, fig. 13, 
allows what often occurs in Smerinthus and Pygaera. 
