Cuap. II. SEGMENTATION OF THE YOLK. 525 
hardly older than the second one, (PI. 10, fig. 1 and 2,) but much more. irregular, 
(Pl. 10, fig. 4,) evimeing a great want of symmetry in the origin of the trans- 
verse lateral furrows, so much so that on one side a small segment mass had 
become totally isolated by a circumyallation. 
The embryonic area of the three following eggs, two of which were from the 
left (Pl. 10, fig 6 and 7) and one from the right (fig. 5) oviduct, exhibited 
about the same degree of advancement: all agreed in being very irregular in 
their segmentation, and in having most of their furrows more or less transverse to 
the longer axis of the yolk, without any trace of the principal furrow observed 
in the younger stages. Centrally each possessed two or three isolated masses, 
and others more or less completely separated. It would be almost a needless 
repetition, after what has already been shown, to insist here upon the centri- 
fugal character of this process, as the first isolated masses originate always at 
the centre of the embryonic layer, and those which appear afterwards are suc- 
cessively further and further out of the centre. This is more particularly notice- 
able in another embryonic area, (PI. 10, fig. 8,) the fourth and last in the left 
oviduct of the same animal, which is still further segmented, and in which the 
furrows radiate from a centre occupied by five isolated masses, while the cone- 
like portions included by these furrows are more or less rounded off at their 
summits. In this same egg, too, we may observe the diversity in size at which 
the masses originate, two or three being much smaller than some others, that 
are more central. 
On the 28th of May another Turtle was opened, and, as already stated, the 
eggs were found in a very advanced state of segmentation, yet not so far 
beyond those of the first animal opened the day before as to break the link 
of connection with them. The segmentation had already extended over a much 
larger extent than the furrows of the embryonic areas observed the day before 
had included, and the now numerous radiating cones diverged from a field still 
more distant from the centre (Pl. 10, fig. 9, 10, 11, Ila, 11b). Of four embry- 
onic areas in this condition, that in the oldest egg, (Pl. 10, fig. 9,) the fourth 
and most posterior in the right oviduct, was the least evenly segmented; the 
centre being still occupied by several masses larger than those embraced in the 
same region in the other three. However, all four agreed with each other in 
having the most minute masses in the centre, and the larger ones at the cir- 
cumference. But the furrowing had not altogether taken place in a_perpendic- 
ular direction, as we may see by a glance at one of the more magnified views, 
(Pl. 10, fig. 11,) where the masses are heaped one upon the other in such a 
manner as unmistakably to evince a horizontal fissuration, such as was partially 
approximated in the oblique chasms of the earliest segmentation (PI. 10, fig. 
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