618 EMBRYOLOGY OF THE TURTLE. Part III. 
ular, rounded appearance. By maceration in water, the membranous sheath of the 
fibres (fig. 24, and a) becomes quite conspicuous, and distends so as to leave 
the mass of disturbed fibrille floating free in the centre. Just before birth, the 
muscular fibres of the upper retractor muscle of the head are very transparent — 
(fig. 27). When the fibrille are not disturbed, they are excessively transparent, 
and represented by the light spaces between the faint, parallel, longitudinal lines 
which may be seen in every part of the fibre; but where they are displaced, 
their component granules are separated or dislocated, and thrown into zigzag 
lines (fig. 27a). The granules are then easily recognizable. Treated with very 
weak alcohol, the undisturbed fibrille gradually display their component granules 
in close and continued series. Where the granules had been disturbed and_sep- 
arated from each other, before the application of alcohol, spaces were left between 
them, as the application of this reagent proved. 
The Tendons. A short time before birth, the tendons of the foreleg consist 
of very slender, spindle-shaped cells, packed closely together (fig. 26, 26a). They 
do not appear to have united, as yet, to form the slender fibrille of the adult 
tendon. 
Seu C AOI nc. 
CHRONOLOGY OF THE DEVELOPMENT OF THE EMBRYO. 
In the higher Vertebrata, the progress of the embryo is generally so regular, 
that the investigator, knowing the period of gestation or of meubation, is at the 
same time certain to find the different parts of the germ proportionally developed. 
This is not the case with the Testudinata, at least not so strictly; since the embry- 
onic growth may be retarded for weeks, and the period of hatching postponed for 
months. In order, therefore, that the reader may see at a glance what figures 
belong to any particular phase, we give below a list of our figures, arranged 
according to their actual degree of development, in stages, and have affixed the 
dates of the time when the eggs were laid, and when they were opened and 
drawn. By this, it may be seen that age tells very little respecting the real 
degree of development of the embryo; but that the actual imspection of the 
structure of the organs is necessary, in order to ascertain whether any two or 
several embryos are equally developed. The duration of the growth of the ova- 
rian eggs has already been discussed. (See p. 490 and 496.) For the names of 
the different species, see the Explanation of the Plates. 
First Stage. Pl. 10, fig. 12, taken from the oviduct and drawn at once, June 

