532 EMBRYOLOGY OF THE TURTLE. Part III. 
suffice here to say, that it will there be found to bear a relation to the body and 
the whole system different from that which has usually been supposed or admitted. 
When we look at the cellular tissue of the lower branches of the animal king- 
dom loosely strung together, where we may see every cell of a muscle dilate 
and contract for itself; where, in the younger but free stages of the same, these 
cells hardly touch each other, and yet dilate and contract; where the whole 
animal moves from place to place by the help of these selfsame active vesicles ; 
or where, in the simplest phases of organic structures, we may actually count the 
number of cells of which the body is composed, as the animal flutters and 
quivers while fallmg to pieces before our eyes;— when we see all these phenom- 
ena, we need not fear to adopt views contrary to a sound physiology im advo- 
cating the animality of the yolk,‘ notwithstandmg the loose connection of its 

1 We need only refer to the researches of Brs- 
corr, upon the Embryology of Mammals (Entwicke- 
lungsgeschichte des Kaninchen-Eies, q. p. 83: p. 98, pl. 
8, fig. 40 D, and pl. 16) —Barr, upon Birds (Uber 
Entwickelungsgeschichte der Thiere, q. p. 67: Er- 
ster Theil, p. 67, pl. 1, 2, p1, 77, t, wu, s1, g') — Remax, 
upon Batrachians (Untersuchungen iiber die Entwicke- 
lung der Wirbelthiere, q. p. 83: p. 81, pl. 10, fig. 1-5, 
pl. 12, fig. 1-8) — Voe, upon Fishes (Embryologie 
des Salmones, in Agassiz Histoire naturelle des Pois- 
sons d’ eau douce de l Europe centrale, q. p. 81: 
vol. 1, p. 38, pl. 5, fig. 116-120) — KoOriixer and 
Zappacu, upon Insects (K6lliker, Observationes de 
prima Insectorum Genesi, q. p. 80: p. 8, sect. 4, 
pl. 1, fig. ii., 1, 3, p. 12, sect. 18, pl: 2, fig. i, 1, 3); 
Zaddach, Untersuchungen iiber die Entwickelung und 
den Bau der Gliederthiere, q. p. 80: I. Heft., p. 3 
and 4, sect. 2 and 3, pl. 1, fig. 2, 3, and 4, C, fig. 5, 
K) — Raruke, upon Crustacea (Zur Morphologie, 
Reisbemerkungen, q. p. 79: p. 74 and 7), fig. 9, 
10, 11) —Mitne-Epwarps, upon Annelides (Re- 
cherches anat. et zool., q. p. 
p» 34-36, fi 
92: premitre partie, 
g. 47-50) — KOxLiiker, upon Cephalo- 
poda (Entwickelungsgeschichte der Cephalopoden, q. 
p- 74: p. 165, pl. vi. fig. lx.—lxiii.) — Guern- 
BAUER and LreypiG, upon Gasteropoda (Leydig, in 
Zeitschrift fur Wissenschaftliche ZoGlogie, q. p. 73: 
p- 150, pl. xi. fig. 5-8 ; Gegenbauer Untersuchungen 
iiber Pteropoden und Heteropoden, q. p. 74: p. 66, 
pl. iii, fig. 9-15, and p. 179, pl. viii, fig. 3-9) — 
QUATREFAGEs, upon Acephala (Annales des Scien- 
ces Naturelles, 1859, tome xi., p. 208-215, pl. 9, 
fig. 16-26) — Derbes, upon Echinodermata (Annales 
des Se. Nat., 1847, tome 8, p. 90-92, pl. 5, fig. 6-14) 
— Sresotp, upon Medusa (Neueste Schriften der 
Naturforschenden Gesellschaft in Danzig, 1859, p. 
22-29, sect. 14-28, pl. 1, fig. 12-19), —and a host of 
other authors, quoted in connection with a former 
section, (see p. 68-87,) to furnish abundant evidence 
of the truly internal position of the yolk. This part 
of the egg is, from the beginning, embodied within 
the extended layers of the embryo, “the germinal 
layer.” In some instances it even assumes very early 
an organic form, (see Remak, loc. cit., pl. 10, fig. 19- 
23, dk, and dk, pl. 12, fig. 10, dk; Dr. J. Wy- 
man on the Surinam Toad, Sill. Journ., May, 1854, 
p- 371, fig. 3; Leydig, loc. cit., fig. 8-12, b, ce, d, g; 
Milne-Edwards, loc. cit., p. 24-26, pl. 1, fig. 8-11,) 
although its components are quite loosely attached to 
each other. It may be said that the extension of the 
germinal layer around the whole yolk mass does not 
sufficiently imply the identity of the latter with the 
rest of the embryo; yet, when we see this same mass 
take the form of an important organ, especially well 
marked in the Surinam Toad, (Pipa americana,) and 
so ably described in Wyman’s investigations upon this 
animal, in which the whole yolk is shaped into a 
spiral intestine, there is no longer any reason to re- 
sist the conclusion, that this portion of the living 
mass is as fully subject to that plastic power which 
