160 Proceedings of the Royal Society of Edinburgh. [Sess. 
into daughter spindles ; while fig. 2b suggests the presence of a small 
independent spindle, with smaller chromosomes, much massed, though 
tending into two groups. The question arises whether this small spindle has 
arisen from the outer daughter nucleus of the first polar body ; but, on the 
evidence furnished by this one egg, it would be rash to say whether there 
be one, two, or three spindles, and 1 hope, when material again becomes 
available, to make a further study of this interesting point. The rather 
scattered chromosomes of the larger spindles exist for the most part as 
dyads or tetrads, but one or two seem to be more elongate. The chromo- 
somes of the small spindle are packed more closely than is shown in 
the figure, and it is impossible to define the outline of many of them, but, 
judging from those that are isolated, they appear similar in form to the 
larger ones. At the stage when four amoeboid cells exist in the yolk, the 
spindle threads have vanished, but the chromosomes may yet be seen. 
In later stages they also have disappeared. 
The Formation of the Germ-band from the Ventral Plate. 
After the completion of the blastoderm, the next change that occurs in 
the developing egg is the differentiation of a portion of the blastoderm to 
form the ventral plate or germ-rudiment. This area occupies about one- 
third of the ventral surface and, continuing round each side, overlaps the 
dorsal surface to the extent of about one-quarter of its width (figs. 6a 
and 6b). The figure so formed, if straightened out, would form an oblong, 
with its rounded ends rather broader than its central region, and its position 
is always somewhat nearer to the caudal than to the cephalic end of the 
egg. The cells composing this embryonal area or ventral plate form a one- 
layered columnar epithelium (fig. 6c), while the cells of the remainder of 
the blastoderm have become much flattened. Stained by eosin and toluidin 
blue and decolorised, sections show that the blastoderm cells readily part 
with the blue stain, while the rich cytoplasm of the cells of the ventral 
plate bolds it tenaciously. 
At the margins of the ventral plate the amnion fold arises, the cells of 
the fold being similar to those of the ventral plate, so that at this time there 
is no clear line of demarcation between amnion and ventral plate. The 
amnion grows over the lateral portions of the ventral plate and over the 
ventral surface of the latter, the margins of the amnion fusing mid-ventrally. 
Thus the amnion and the ventral plate together form a closed sac which 
separates from the serosa (the epithelium now covering the egg) and sinks 
into the yolk. A transverse section of an egg where this process is just 
beo-innino' is shown in fig. 6c. The amnion fold has commenced to form at 
