Agassiz on the Embryology of the Turtle. 347 
48 formed by a stratification of the inner cells of the Graafian 
_ follicle, and therefore is not developed inside of the yolk sac, as. 
_ fas been asserted of it by some authors when treating of its 
_ gin in the eggs of other animals. Eventually the zona ap- 
_ Pears as if made up of columnar cells, and thus remains. during 
_ the rest of its existence. It may be detected even as late as 
yer, originating by a transformation of the superficial part of 
the yolk when the égg is hardly visible to the naked eye, and 
the formation of an excessively transparent cellular tissue, which 
ticed in the eggs of animals, but when the embryo has begun 
0 develop, it occupies the same relative position as the “Keim- 
base” of Bischoff, or the “ Umiiillungshaut” of Reichert, and the 
‘gion of the embryo and even becomes a lining to the spinal 
tube. At the time the turtle is hatched this membrane may be 
detected as readily as in any of its earlier stages. 
Feeundation.—Professor Agassiz’s observations are so remark- 
able, and the facts in regard to fecundation so unprecedented, 
‘at I think it worth while to quote here the whole of the sec- 
tion he has written on this subject. 
“Ever since I have known that our Turtles Jay only once a year, I 
ve been struck with the fact that the ovary nevertheless contains eggs 
 « 
of Birds 
Tesearc| ) 
animals, in i 
Where he describes the zona as the original yolk-sac and the ae hate a 
; stratum o . ‘ 
Yello . i calls it, havi 
ow yolk granules, (the primary se zona Laegy i nistak sit, having 
oe si ; ' : 
Upposes, but without direct research, that the ‘pellucid space’ because of its 
pr of hexagonal t 
