222 
IOWA ACADEMY OF SCIENCE 
The shortest period in which any hatched was about seventy-five hours; the 
longest period was about 110 hours. The time of incubation seemed to depend 
almost entirely upon the temperature and sunshine. Those kept at a tempera- 
ture above 80 degrees P. and in the sunshine developed most rapidly, while 
those which were away from the light and cooler developed more slowly. 
In those egg masses which were kept in conditions such that they developed 
more slowly there were found more eggs which did not hatch. This would 
seem to indicate that any considerable reduction of temperature or deprivation 
of sunlight would entirely prevent development. No accurate observations 
were made, however, upon this point. 
D. THE EGG. 
The eggs are elongated-oval appearing slightly larger at the extremity which 
is to become the anterior, when viewed dorso-ventrally. When viewed from 
the side they appear more convex on the side which is to become the ventral, 
the dorsal side in the majority of cases appearing slightly concave, through part 
of its length. (See fig.) 
The eggs vary somewhat in size. Prom a number of measurements, the 
average size was found to be very close to 1-21 inch in length by 1-50 inch in 
thickness. Prom these measurements individual eggs varied as much as 1-240 
inch in length and 1-500 inch in thickness, or very nearly 10 per cent. 
The choroin is perfectly transparent, and sornewhat flexible, allowing the 
egg to be distorted by pressure from the cover glass, without breaking. After 
hatching the empty shell was quite flexible. No micropile was observed. 
The vitelline membrane does not fit against the choroin at all points, but is 
drawn av/ay at the ends, usually more at the posterior end. 
The egg contents are composed almost entirely of the nutritive yolk sub- 
stance. There is very little of the outer protoplasmic layer present (keim- 
hautblasten of Weisman). The yolk has a yellowish green color, is very 
granular, and highly refractive. Numerous oil globules of varying size can be 
seen scattered through it. In some of the eggs collected late in the season the 
yolk had a more brownish color. They seemed to be identical with those 
previously obtained in other respects. Only a few of these were obtained and 
it was not determined whether they belonged to different species, or the change 
in color was due to the lateness of the season. 
E. EAKLY STAGES IN DEVELOPMENT. 
The first change noticeable was a slight drawing in of the vitelline mem- 
brane at each end. Shortly afterward there appeared at the anterior end four 
rather large, quite granular cells (PI. 1, fig. 1-a). About an hour later other 
cells not so large began to appear on the surface of the yolk. These form a 
layer (PI. 1, fig. 2) which increases in thickness and number of cells by addi- 
tion from within, until an irregular layer of cells, the blastoderm, of com- 
pard'tively considerable thickness, covers the entire surface (PI. I, fig 3.) 
The cells then arrange themselves regularly and form a layer of columnar 
cells, the blastoderm covering the yolk. During these changes the large cells 
are at all times distinctly visible at the anterior end of the egg (PL 1, figs. 2, 
3 and 4-a). When the formation of the blastoderm begins, the egg contents 
crowd out to the end, entirely filling the cavity of the shell. 
