No. 3.] THE CLEAVAGE OF AMPHIBIAN OVA. 4II 
example, there is a considerable lapse of time between the 
appearance of the first furrow in either set and the last furrow 
in the same set. Even in the third set we have observed so 
long a period as thirty minutes between the appearance of 
furrows in different quadrants (Figs. 12, 18). This tendency 
to divergent rhythm of cell-division brings it to pass that the 
last cell-division in one group falls nearer and nearer in time 
to the first cell-division in the next group, and in this way the 
distinction between ‘“sets’’ of furrows is eventually lost. (See 
Figs. 4, 13, 19, 28, 32, etc.) Up to the point to which we 
have been able to follow the cleavage, however (Amblystoma 
10th set), the general synchronism of division is maintained, 
and the furrows appear closely one after the other; then there 
is a marked pause before the next cell-division. 
The question as to the “homology” of the third Teleostean 
furrow with the first equatorial furrow of the Amphibian egg 
has given rise to some difference of opinion. Some authors 
(Agassiz and Whitman, '84; Ziegler, '87) regard the first three 
furrows in the two groups as equivalent. Others (Rauber, '83; 
H. V. Wilson, '91) believe that the first equatorial furrow in 
the frog has been “lost” in the Teleost. Our observations on 
Amphibian cleavage bear, we think, directly on this point. 
We have found that the third set of furrows, which is usually 
horizontal, may sometimes be truly vertical in one, two, three, 
or even all four quadrants. (See Figs. 2, 8, 26, 33, etc.) 
That in these cases there is any “loss” or “dropping out”’ of 
furrows is obviously absurd, especially since the third set, 
when thus irregular, appears simultaneously with the “normal 
equatorial” of other eggs from the same parent. Now, since 
the third set of furrows in the Amphibia is sometimes truly 
vertical, there is no occasion for surprise that the third set in 
the Teleost egg is normally vertical. To speak of any ‘“loss”’ 
of the third set of furrows in Teleosts, seems not only vague 
but meaningless. It is not at all remarkable that the spindles, 
under the different conditions prevailing in the Teleostean egg 
should take up a position different from that taken in the Amphi- 
bian egg. In the Amphibian egg itself, as we have shown, they 
are free to take a variety of positions even at the third division. 
