Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 
De- 
* |signation 
Preparation Data 
Body Form 
! Somites 
Head-Somites 
13 
14 
15 
16 
17 
19 
HE.C. 
994 
H.E.C. 
980 
H.E.C. 
H.E.C. 
1499 
H.E.C. 
939 
H.E.C. 
1498 
H.E:C. 
1398 
H.E.C. 
1497 
Fixative: Aceto-corrosive. 
Section: Sagittal, 6 ». 
Stain: Borax carmine, orange G. 
Fixative: Aceto-corrosive. 
Section: Transverse, 6 ». 
Stain: Borax carmine, orangeG. 
Fixative: Aceto-corrosive, 
Section: Transverse, 6 x. 
Stain: Borax carmine, safranin. 
Fixative: Aceto-corrosive. 
Section: Transverse, 6 u. 
Stain: Iron haematoxylin, 
Congo red. 
Fixative: Aceto-corrosive. 
Section: Transverse, 6 u. 
Stain: Borax carmine, Lyons 
blue. 
Fixative: Aceto-corrosive. 
Section: Transverse, 8 u. 
Stain: Iron haematoxylin, 
Congo red. 
Fixative: Aceto-corrosive. 
Section: Transverse, IO u. 
Stain: Iron haematoxylin, saf- 
ranin. 
Fixative: Chromo-acetic. 
Section: Transverse, 6 y. 
Stain: Iron haematoxylin, 
Congo red. 
Anterior sixth of embryo sepa- 
rated from blastoderm, and tur- 
ned a little to the right. Caudal 
swellings as in preceding stage 
(No. II). 
Head and a little of anterior 
part of trunk of embryo sepa- 
rated from blastoderm, and tur- 
ned to the right. Caudal:swel- 
lings longer and narrower than 
in preceding embryos (Nos. II 
and 12). 
Head and a little of trunk of 
embryo separated from blasto- 
derm. Head bent ventrally. 
Head and pharyngeal region 
separated from blastoderm. 
Head bent ventrally at right 
angles to pharyngeal region. 
Incisura neurenterica sharply 
marked. 
Anterior fourth and posterior 
eighth of embryo separated 
from blastoderm. Head bent 
ventrally at a little more than 
right angles to pharyngeal re- 
gion. Incisura neurenterica com- 
pletely enclosed. 
Anterior two-fifths and pos- 
terior one-fifth of embryo sepa- 
rated from blastoderm. Pharyn- 
geal region bent a little ven- 
trally from trunk. Head bent 
ventrally at an angle of 60° to 
pharyngeal region. 
Embryo connected with blasto- 
derm by a little more than its 
middle third. Tail and pharyn- 
geal regions bent a little ven- 
trally from trunk. Head bent 
ventrally at an angle of 60° to 
pharyngeal region. 
Embryo attached to blasto- 
derm for two-fifths of its length. 
A decided dorsal flexure over 
attachment. Head bent nearly 
at right angles to dorsal line 
of pharynx. Tail bent a little 
ventrally to trunk. Slight en- 
largement of tail knob. 
Thirteen pairs of somites (counted from 
sections), fourteenth forming posteriorly. 
Fifteen pairs of somites (counted from 
sections). Vertical diameter of anterior 
somites greater than in preceding stage. 
Mesial walls of anterior two or three pairs 
of somites thicker than lateral. 
Sixteen pairs of somites, seventeenth for- 
ming posteriorly. Last inter-somatic cleft 
lies approximately 200 u. anterior to incisura 
neurenterica. 
Fifteen pairs of somites. A very slight 
outpouching of lower half of mesial wall 
of somites in anterior trunk region to form 
sclerotome. Dorsal to this outpouching, 
mesial wall thickened, obliterating upper 
part: of myocoel. 
Nineteen pairs of somites (counted from 
sections). In cardiac region, sclerotomic 
bud expanded mesially until in contact with 
notochord. Distinct line of differentiation 
between dorsal boundary of sclerotomic 
bund and myotome. 
Twenty-five or twenty-six pairs of somites 
(by 'sections), Segmented mesoderm ex- 
tends to cloaca. No myocoel in posterior six 
pairsof somites. In posterior oesophageal 
and cardiac regions, somites possess definite 
solid sclerotomes, which may extend dorsally 
nearly to dorsal surface of notochord. Myo- 
coel obliterated in dorsal half ofthese somi- 
tes. Inanterior yolk stalk region, sclerotomes 
represented by outpoutchings of the lower 
half of the mesial wall of somites. In pos- 
terioryolk stalk and trunk regions, no trace 
of formation of sclerotome, — mesial and 
lateral walls of somites of equal thickness. 
Twenty-six or twenty-seven pairs of somites 
(counted from sections). Anterior somites 
well differentiated in sclerotome, myotome. 
and dermatome. Anterior to middle of 
trunk, scierotome differentiated and myo- 
tome thicker than dermatome. Cells of 
myotomes of anterior ten somites elongated 
until nearly filling myocoel. Sclerotomes 
becoming slightly mesenchymous. In five 
anterior somites, sclerotome extends upward 
to dorsal surface of notochörd. 
Thirty-three somites (counted from sections). 
Segmented mesoderm extends as far as pos- 
terior boundary of cloaca. In cardiac and 
in anterior half of yolk stalk region, sclero- 
tomes mesenchymous. 
Mandibular somite separated 
from posterior mesoderm dor- 
sally, broadly connected ven- 
trally. A small lumen in hyoid 
somite. 
Mandibular somite completely 
cut ‚off dorsally from the pos- 
terior mesoderm, much dilated 
anteriorly, compressed pos- 
teriorly. Hyoid somite broadly 
connected with the posterior 
mesoderm. 
Mandibular somite consists of a 
greatly dilated anterior portion 
and a flattened ventral process 
which is attached to the general 
mesoderm by a narow stalk. 
Hyoid somite somewhat dilated, 
but still connected posteriorly 
and ventrally with the general 
mesoderm. 
Mandibular somite connected 
with hyoid somite by a few 
cellular strands. 
Anterior end of mandibular 
somite much expanded. Vertical 
diameter of stalk connecting it 
with general mesoderm is one 
third that of somite. Small 
cavity in hyoid somite. Hyoid 
somite separated from mandi- 
bularbynarrow .cleft. Connected 
with general mesoderm by two 
bands ofmesoderm, one passing 
down second gill arch and one 
over second gill pouch. 
Mesial walls of mandibular 
somites much thickened, slightly 
mesenchymal. A cellular bridge 
connects the two somites just in 
{rontofnotochord. Hyoidsomite 
connected with the mandibular 
somite for one section (6 &) on 
the left and two sections on the 
right side. Anterior somite a 
distinct solid process extending 
dorsally and laterally from pre- 
oral mesoderm. 
Mesial part of premandibular 
somite attached to floor of pre- 
oral gut. A small cavity in each 
lateral enlargement of the 
somite. Lateral walls of en- 
largements epithelial. Three ir- 
regular cavities in median stalk, 
just below end of notochord. 
Stalk of mandibular cavity 
elongated as compared with 
preceding embryo (No. 16), its 
vertical diameter approximately 
one-fourth that of expanded 
anterior portion. 
