ON DEVELOPMENT OF ATYEPHIEA COMPRESSA. 
409 
two equal parts (tigs. 19 and 20). After remaining in this 
condition for about two or three hours, the segmentation line 
becomes narrower, the two halves gradually approaching each 
other, and at last the egg is again in a condition not externally 
different from that which Ave started (tig. 23). Internally, 
however, we see the nuclei clearly separated from each other, 
and these are sometimes in the state of division, showing thus 
the commencement of the second or the longitudinal furrow. 
After resting three to four hours more, the first line becomes 
visible again (fig. 24). It soon divides the egg into two equal 
halves as before. Immediately after (5 — 12 minutes) the 
second line of division makes its appearance at right angles 
to the first and divides the egg into four equal parts (fig. 26). 
This line generally makes its appearance first on one half 
close to the first furrow, and is soon followed by a corre- 
sponding line on the other half. They travel in opposite 
directions, until they meet with each other on the other side 
of the egg. Sometimes, as an exceptional case, two lines of 
the second furrow appear simultaneously on the two halves of 
the egg close to the first furrow at a distance of 90° from each 
other. These divide the egg into four equal parts as before, 
but only with this difference, that the four segments do not 
lie in the same plane. This irregularity is, however, soon 
lost in the next stage, when the division of the egg proceeds 
up to eight segments, the second vertical furrow appearing at 
the distance of 90° from the first vertical furrow. About two 
hours after the egg has been divided into four parts, the 
second line becomes narrower, and the four divided parts 
again coalesce into two. Some time later, the first transverse 
furrow becomes also fainter, and the egg apparently retro- 
grades to its first stage before segmentation, with the difference 
of having four nuclei instead of one (figs. 2 7 and 28). At 
the end of a short period of repose, the nuclei prepare to 
divide, and with this the original furrows are again restored 
in order of their appearance, soon followed, this time, by the 
second set of longitudinal furroAVs dividing the egg into eight 
equal parts (figs. 30, 31, 35, 36, and 37). 
