Cuap. II. SEGMENTATION OF THE YOLK. 523 
SCL Ome Ve: 
SEGMENTATION OF THE YOLK. 
The morning of the 27th of May, 1854, was made memorable to us, in our 
investigation of the embryology of Testudinata, by the discovery of the segmenta- 
tion of the yolk in eggs of Glyptemys insculpta. After repeated trials every 
day for the space of several weeks upon Chrysemys picta, Nanemys guttata, Ozo- 
theea odorata, Chelydra serpentina, and Cistudo virginea,— which were opened in 
great numbers, sometimes a little too soon, when the eggs were still in the 
ovary but just about to drop from it into the oviduct, or again too late, 
when the embryonic area had already obtained its definite outlme and smooth, 
uniform surface,—it seems rather singular, that a species which is comparatively 
rare should have furnished the information so long looked for. 
From what was seen in the oviducts of one of these animals, it is evident 
that the segmentation of the yolk proceeds very rapidly, imdeed so rapidly, that 
the space of twenty-four hours probably covers the greater extent of this process. 
Of three animals opened in three successive days, the first furnished eggs, on 
the 27th of May, exhibiting the earliest stages of segmentation thus far observed 
in Turtles (Pl. 10, fig. 1-8); the second, on the 28th of May, gave those in 
which segmentation was almost completed (Pl. 10, fig. 9-11b); and the third, 
on the 29th of May, contained only eggs with well defined embryonic discs 
(Pl. 10, fig. 15, 15a). After all, we were not favored with the view of a 
primitive furrow, dividing the yolk into two equal portions. There is even good 
cause to doubt that the yolk always commences segmenting in such a regular 
manner, if we may judge from the total absence of bilateral symmetry in some 
of the early stages of this phase (PI. 10, fig. 5, 6, 7) in the development of the 
ego. The youngest and simplest form of segmentation was observed in the most 
anterior of three eggs, in the right oviduct. About midway between the two ends 
of the yolk mass, which was already elongated,—as in fig. 1 and la, which repre- 
sent a similar but somewhat older state,—and parallel to its longer axis, there 
ran a straight, narrow, and deep furrow, (Pl. 10, fig. 3,) with rounded edges, broad- 
ening at each end, and shallowing to a level with the surface of the more 
eccentric segments. Altogether this furrow equalled in length a little more than 
one fifth of the longitudinal diameter of the vitelline mass. (Compare fig. la, 
to see the natural size.) Commencing at two points, a little more than one 
third the distance from the ends of the first furrow, other furrows of a similar 
