112 M. Ussow’s Zoologico-Embryological Investigations. 
also the first germ-lamella is thickened (especially at the sides 
and on the dorsal surface) by its cells dividing rapidly in the 
longitudinal direction, by which means they become higher 
and cylindrical. 
This part is followed immediately by the rather narrow 
girdle-like part, originating from the segmentation-spheres 
uniformly separated by constriction from all the thirty-two 
segments, which occupies the equator of the vitellus, and is 
bounded above by the middle portion (the future trunk of the 
animal), and below by the blastoderm (rudiment of the yelk- 
sac), which is everywhere uniformly thin, two-layered, and 
closed at the inferior pole. In the above-mentioned peripheral 
girdle-like portion of the spherical germ the cells are broad, 
but at the same time flat; so that this part is as thin as the 
rudiment of the yelk-sac. At the end of the first period all 
the cells of the upper germ-lamella are distinguished only by 
their height and breadth ; as regards their form there is nothing 
peculiar to certain parts of this germ-lamella. There are cells 
with three or four angles, and with them others with five, six, 
seven, or even eight angles. 
2. The second or middle germ-lamella, which attains its 
greatest thickness at the oval fold, and splits into two layers, 
the dermo-muscular layer and the intestino-fibrous layer. 
With the development of the germ this cleavage of the 
middle germ-lamella increases both by the transverse division 
of its cells and also by the spreading of the two layers, which 
takes place in the direction from the rhomboidal centre towards 
the yelk-sac. 
The two layers of the second germ-lamella show the follow- 
ing characters :—a. The dermo-muscular layer (Hautmuskel- 
schicht) thickens somewhat in the central part of the blasto- 
derm and in the girdle-like ring situated on the equator of 
the vitellus ; by the continued gradual division of the cells of 
the blastoderm (see the commencement of the formation of the 
second germ-lamella), and by the imdependent longitudinal 
division of its cells, this layer grows pretty rapidly beneath the 
upper germ-lamella and becomes closed at the inferior pole of 
the nutritive vitellus. 6. The intestino-fibrous layer (Darm- 
faserschicht), as the development of the germ goes on, occurs 
not only on the ventral surface (below the oval annular fold 
of the rhomboidal centre), but its rather loose cell-series, lying 
immediately upon the nutritive vitellus, also increase towards 
the dorsal surface in the middle part of the germ. Various sec- 
tions from earlier stages (e.g. of the tenth day) show that 
the cells of the intestino-fibrous layer accumulate most on the 
sides of the longitudinal axis of the germ, namely where the 
