570 L. DONCASTER. 
remain for a short time longer flattened against the edge of 
the egg. Immediately after the second maturation mitosis 
the innermost nucleus begins to move deeper into the yolk, 
and, at the same time, towards the anterior end, so that at 
the time of the fusion of the polar nuclei it is found several 
sections further forward, closely embedded in yolk granules. 
The distance which it travels varies somewhat in different 
eggs, but about at the time when the chromosomes of the 
“copulation-nucleus” have separated into two groups it 
begins to divide, and in a short time numerous nuclei are 
found scattered in the yolk, especially in the front half of 
the egg. These “yolk-nuclei” are generally embedded in 
little masses of protoplasm, which makes them easy to find. 
I have not succeeded in finding the first division spindle of 
the egg-nucleus, but at a slightly later stage mitotic spindles 
are abundant, and differ considerably in form from the polar 
spindles. They are smaller and much narrower, so that the 
chromosomes are closely packed together, but the chief 
difference is that in the yolk-mitoses there are very con- 
spicuous centrosomes, of which I have seen no trace in the 
polar mitoses (Pl. 36, fig. 32). Since the earliest stage of the 
division of the egg-nucleus that I have found consists of two 
nuclei lying near together just after division is completed, I 
cannot say at exactly what stage the centrosomes first appear. 
Another point of considerable interest is that im the seg- 
mentation mitoses the chromosome number remains the same 
as it is in the maturation divisions; this is seen clearly when 
a mitosis in the yolk is cut across transversely (fig. 26). 
Several hours after the egg is laid, when the yolk nuclei 
have become very numerous, they begin to come to the 
surface and form a blastoderm, just as in other insect eggs. 
In the blastoderm nuclei a deeply-staining nucleolus is 
commonly found; it appears to consist of chromatin, and 
may be double. I have not seen it in stages younger than 
about fifteen or twenty hours, 
