533 
Bearp believes that the grooves extend to the lower pole, like those 
of the first and second cleavage. DEAN says that “in depth and 
lateral extension its furrows are entirely similar to those of earlier 
cleavage”. 
Fig. 2. 2 hrs. 48 min, after fertilization. Fig. 3. 37/, hrs. after fertilization. 
The fourth cleavage, as stated by Dean, “is again a vertical one”. 
The eight grooves forming this cleavage generally occupy the positions 
shown in Fig. 3. In all eggs examined but few exceptions were found, 
the few showed one or more of the grooves passing in a circular 
direction. These grooves extend to the region of the equator and 
here fade out. Concerning the extent of this cleavage we have no 
previous observations beyond those of DEAN who figures and describes 
it as “similar in its limits to the third cleavage”. 
With the formation of the fifth cleavage most interesting changes 
are introduced. It comprises two distinct sets of grooves, one set 
appearing in the twelve marginal cells, shown in Fig. 3, while the 
other set divides the four central cells of Fig. 3. The greater number 
of the first set pass in meridional planes; one often, however, observes 
a part of the grooves following the direction of a circular cleavage. 
The grooves which divide the four central cells pass in horizontal 
planes and of course are not visible on the surface. The fifth cleavage 
thus gives rise to the usual 32 cells. It would be an error to think 
of this cleavage as following a given type, numerous variations occur, 
which are so diverse that no attempt has been made to record them. 
Were one to give a general plan, it would seem to be that outlined 
above. 
Fig. 4 represents an egg in about the sixth or seventh cleavage. 
It is quite impossible at this time to trace the furrows as they appear 
