Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 
| 
No. | 
Nose 
Ear 
Integument, Lateral Line 
Mouth 
Arch- 
enteron 
Pharynx, Thyreoid, Thymus, 
Suprapericardial Body 
12 |As preceding stage (No. 
rs 
| 
| 
13 ‚As preceding 
stages 
(Nos. II and 12). 
14 | Optic vesicles extendpos- 
teriorly 40 u (by sections) 
from fore-brain. Expan- 
ded laterally, dorsal walls 
extending outward nearly 
at right angles to walls 
of fore-brain. 
15 |Like preceding 
(No. 14). 
stage 
16. | Optic vesicles broadly 
expanded anteriorly and 
dorsally. 
17 |Optic vesicles extend for- 
ward 32 u. (by sections) 
from attachment to fore- 
brain. Anterior half of 
dorsal wall slightly over- 
laps fore-brain. 
18 | Optic vesicles decidediy 
expanded anteriorly and 
dorsally. Optic stalk nar- 
rower than vesicle — pos- 
terior wall of stalk pro- 
jects at right angles from 
fore-brain. 
ı9 |Ectoderm slightly thick- 
ened, forming a lentic 
plate over optic vesicles. 
Optic vesicles much ex- 
panded dorsally and cra- 
nially. Lateral surface of 
vesicles flatly concave, 
Optic stalks one-third as 
long, and one-half as 
wide as vesicles. 
Nasal placodes 
a pair ofdistinct 
thickenings of 
epithelium 
lying on either 
side of the 
closed ventral 
(anterior) end of 
neuropore, and 
ventral to the 
optic vesicles. 
Like preceding 
stage (No. 18). 
Ectoderm a little thickened on 
either side of medullary tube 
Just posterior to first gill pouch. 
15 „u. in thickest part. 
Thickening of otic placode lies 
over second gill pouch. A little 
more differentiated from skin 
ectoderm than in preceding 
stage. Greatest thickness 35 u. 
Unchanged from preceding 
stage (No. 15). 
Anterior part of otic placode 
very slightly depressed. 45 u in 
thickness in thickest part. 
Sharply differentiated from skin- 
ectoderm dorsally, other bor- 
ders not sharply marked off. 
Resting nuclei lie in inner part 
of epithelium, leaving a broad 
clear outer zone in which are 
many mitoses. Cells of auditory 
crest fused with ventral part 
of placode. 
A distinct though shallow de- 
pression in anterior and dorsal 
part of otic placode. Epithelium 
of placode thickest dorsally. 
Greatest thickness 80—85 u. 
Deep otic pit in anterior part 
of placode. Anterior wall of 
pit turned inward at right 
angles to skin-ectoderm. Edge 
of anterior part of dorsal wall 
slightly overhanging. Ventral 
and posterior edges pass gra- 
dually over into skin-ectoderm. 
As preceding stages (Nos. Io 
and II). 
Epithelium in tail and trunk 
region IO u thick, nuclei spheri- 
cal and closely packed. In an- 
terior pharyngeal region the 
lateral thickening, described for 
No. 8, extends from a little 
below roof of gut to dorso- 
median line above, 35 y. thick, 
two rows of nuclei. 
As in preceding stage (No. 13), 
except that lateral thickening 
is more definitely outlined. The 
dorsal and anterior portion of 
thickening becoming differen- 
tiated into otic plate. (See ear.) 
Like preceding stage (No. 14). 
(See nose and ear for special 
thickenings.) 
Skin-ectoderm not over I8 u. 
thick in cephalic region except 
around neuropore and where 
sense organs are developing. 
Ectoderm is somewhat thick- 
ened on either side of pharynx. 
This thickening extends pos- 
teriorly as far as anterior part 
of yolk stalk. For epithelium 
ofmedian ridge, see extremities. 
Ectoderm in pharyngeal region 
forms a fairly definite plate 
15—30 u. thick. Cells in this 
region distinct, columnar, with 
elongate nuclei. In posterior 
part of trunk, where still con- 
tinuous with the blastodisc, 
epithelium extremely flattened, 
with elongate flattened nuclei. 
The portion of lateral placode 
not involved in formation of 
otic plate, has become in- 
distinguishable from surround- 
ing epithelium. Otherwise, in- 
tegument as in preceding stage 
(No. 17). 
Epithelium over hind-brain very 
much flattened. Epithelium of 
cephalic region about same 
thickness as that over body. 
Epithelium 
thickened to 
form oral 
plate. Incon- 
tact with 
floor of 
pharynx pos- 
teriorly. 
As pre- 
ceding stage 
(No. 16). 
Oral plate 
slightly de- 
ressed. 
ctoderm 
and ento- 
derm fused: 
As pre- 
ceding stage 
(No. 18). 
Position of first gill pouch in- 
dicated by a slight lateral en- 
largement of pharynx. 
First gill pouch distinct. 
Fore gut approximately 0.3 mm. 
in length. First gill pouch 
distinct. 
Pharynx 325 u in length (by 
sections). Preoral gut extends 
30 u. anterior to pharynx proper, 
opens into pharynx floor 20 u. 
behind anterior wall. First gill 
pouch well established. Second 
gill pouch a shallow groove, 
present on right side only. 
Pharynx slightly larger an- 
teriorly than posteriorly. Two 
gill pouches; first pouch in con- 
tact with ectoderm for over 
half its length; second pouch 
in contact with ectoderm for 
short distance in its middle part. 
Ectoderm and entoderm in con- 
tact over greater part of first 
pouch; fused at cephalic end. 
Cleft of first slit distinctly mar- 
ked externally. Ectoderm and 
entoderm in contact oversecond 
pouch, but not fused. Thyreoid 
ashallow ventral groove in floor 
of posterior-part of pharynx. 
Pharynx expanded anteriorly; 
ectoderm and entoderm fused 
over first gill pouch for one 
half its length. Entoderm of 
second pouch in contact with 
ectoderm for a short distance. 
Thyreoid a distinct pouch from 
floor of pharynx. 
First two gill pouches well de- 
fined, third pouch indicated 
dorsally. Ectoderm and ento- 
derm over first two fused; in 
contact over third pouch. Walls 
of thyreoid sac in contact. 
! 
N 
PB 
