550 EMBRYOLOGY OF THE TURTLE. Part III. 
albuminous fluid, which is totally different in appearance from the blood, contain- 
ing blood corpuscles, which is usually described as indicative of the earliest cir- 
culation! This fluid is set in motion by the impulsive contractions of the heart; 
as may very easily be seen by the help of a low magnifying power. This clear, 
dark area, which we now know to be the vascular area, is considerably increased 
in size beyond the space it occupied when first noticed, (see Pl. 14, fig. 12,) so 
as to have a diameter of about double the length of the embryo, and equal to 
one sixth of the circumference of the egg. 
At the next step, we find the embryo still more bent upon itself, especially 
at the anterior part, (Pl. 12, fig. 6,) where the head curves downwards and 
backwards so as to approximate the cardiac region (4). A greater definiteness 
obtains in the outlines of the eyes (Pl. 12, fig. 6, &; Pl. 21, fig. 28) and ears 
(Bl: 12 fig Giad; yPliy 21, hee eA 7). 
(BL: 12s fig. 18, %e): 
and 13, /). 
increased constriction of the abdominal parietes (fig. 13, 0). 
fi 
and curved downward towards the ventral surface of the body, carryimg with it 
The spinal tube is still more closed over 
The dorsal vertebre are more marked posteriorly (fig. 12, 
The subsidiary layer is still further contracted at its mouth, by the 
The heart, (Pl. 12, 
6, 2,) mm addition to the sigmoid flexure of the last phase, has become swollen 
oO, 
to) 
the superposed musculo-cutaneous layer” At this advanced stage of growth, the 
embryo is so transparent that the whole internal organization may very easily 
be recognized without the help of dissection. This transparency, however, does 
not amount to that glassy clearness which it obtains among the embryos of 
Fishes. The further progress in the evolution of the nervous system, the dorsal 
vertebra, the chorda dorsalis, the eyes, the ears, and the branchial fissures, will 
be described when treating of the special development of each of these organs; 
it being sufficient here to have traced their origin and mode of growth up to that 
period when the nature of each and all of them could be easily recognized. 
Hereafter we shall merely mention the degree of development of these organs at 
each phase, without adding any special details respecting the process through which 
they have passed to arrive at any particular stage, and at the same time describe 

1 This early circulation of an albuminous fluid 
with minute granules probably precedes the forma- 
tion of the blood in all Vertebrates. I have observed 
it in Fishes and Birds. 
? If the embryo is cut out of the ege in connec- 
tion with the vascular area and immersed in sugar 
syrup, it will live, and its heart beat vigorously, for at 
least twelve hours. In some instances, when the 
whole egg was sunk in syrup, after the shell had been 
taken off, the embryo lived not less than thirty-six 
hours. We have several embryos of different ages 
which have been preserved in strong syrup for more 
than two years, and the blood has just as clear and 
brilliant a red color as when it flowed through the 
vessels of the living animal. Caution, however, is 
necessary in transferring the embryo to the densest 
syrup in which it is eventually to be preserved, else 
the animal may shrink and become distorted. 
