SOME PROBLEMS OF COELENTERATE ONTOGENY 505 
show how strikingly irregular and unsymmetrical cleavage may 
be in eggs of a given lot, developing under identical conditions. 
But in these cases the first two of three cleavage furrows are more 
or less symmetrical. In not a few, however, cleavage is dis- 
tinctly erratic from the first, the first furrow dividing the egg 
into very unequal portions. In such cases the irregularity be- 
comes usually increasingly more so as cleavage goes forward. 
A very interesting case is that shown in figs. 9 to 138, which 
occurred at irregular intervals within a period of about forty 
minutes of constant observation during which the sketches were 
made. The egg was kept under observation for several hours, 
or till the morula was apparently completely formed. Fig. 9 
shows what may be regarded as a four-cell stage, the central 
portion comprising the main body of the cell, while at opposite 
poles are three other blastomeres, in each of which the nuclei 
were distinctly visible. In fig. 10 the small blastomere at the 
upper pole has divided, so that now we have a five-cell stage. It 
remained in this condition about fifteen*minutes, when a most 
curious thing happened, the small blastomeres, x and y,being 
the factors of most interest. At first the blastomere y became 
detached from its connection with the cell body as shown in the 
figure, and later the other blastomere x did the same thing, both 
thus becoming absolutely free, in which condition they contin- 
ued about thirty minutes. At the end of this time they resumed 
division and went forward to complete segmentation and formed 
what seemed to be a perfect, though very small morula, shown in 
fig. 11, b. The other portion exhibited something of the same 
tendency. For example, the small blastomere z cut itself free 
as had y, but it later drew back and, fusing with the cell body, 
continued as an integral part of the egg in its later development. 
Figs. 12 and 13 show the general aspects of this portion, which 
went forward normally and became a perfect morula and later 
gave origin to a normal planula. The small segment exhibited 
the same aspects, but later in the day began to show signs of 
degenerative tendency and finally disintegrated entirely without 
assuming the larval condition. ‘This can hardly be ascribed to 
its minute size, for other embryos, which were otherwise appar- 
ently similar in every way, suffered the same fate. 
