NoN2t)  PHEVEGG OF ‘AMIA AND TTS CLEAVAGE. BAN, 
CONCLUDING REMARKS. 
Dr. Dean (No. 3, p. 425) states that he “as taken espectal 
care to verify his observations on the meroblastic character of the 
cleavages of Amia. During the first cleavages several hundred 
living eggs were examined, with a view of determining holoblas- 
tic variations. These, however, did not occur, nor were there 
found, even by the most favorable means of tllumination, traces 
of what might be construed as surface furrows traversing the 
yolk region of the egg. Inno case did a marginal cleavage pass 
below the rim of the germinal disc.” 
If an author can say all this of an egg that is plainly holo- 
blastic, how can we accept his testimony against Balfour, to the 
effect that the egg of Lepidosteus is meroblastic? If this egg 
be holoblastic, its cleavage might be said to agree very closely 
with that of Amia. It would be of interest to know when the 
first horizontal cleavage occurs. Up to the 8-cell stage the 
cleavage grooves may have practically the same order and 
arrangement in Amia, Lepidosteus, Acipenser, and the tel- 
eost. In passing to the 16-cell stage we usually get four cen- 
tral cells, inclosed by twelve marginal ones in the teleost. 
This arrangement, according to Dean’s figures, holds both for 
Lepidosteus and Acipenser. In Amia we get ordinarily the 
circular groove, resulting in eight small cells in the polar (cen- 
tral) field, surrounded by eight large cells. Thus far the three 
eges agree in having no horizontal cleavage. The passage to 
the 32-cell stage introduces, in both Amia and the teleost, the 
first horizontal cleavage; but in the former we have eight cells 
dividing in this way, in the latter, only four. The resemblances 
in other respects would lead us to expect this form of cleavage 
at the corresponding stage in Lepidosteus and Acipenser. In 
that case these ganoids would agree with the teleost in having 
four central (polar) cells thus divided. 
In the more regular forms of holoblastic cleavage, as is well 
known, the first horizontal, or the equatorial, as it is often 
called, comes in as the third cleavage. Is this cleavage, when 
it occurs as the third, homologous with the horizontal, which 
appears as the fifth in the teleost, Amia, and probably other 
