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35. 
Normentafel of the development of the rabbit (Lepus cuniculus L.). 15 
Primitive Segments 
Notochord. Axial Skeleton. Skull 
Externally 5 fully formed segments visible. Segments are small, somewhat 
oblong, but their shape is not very well defined in cross section. 
Externally 6—7 segments. They are now a little larger; their shape in cross 
section is roughly triangular, viz. anterior segments. Small but distinet myo- 
coele. 
Externally about 9 segments. Anterior segments roughly triangular in cross 
section, have a distinct but small cavity. 
Externally 8 fully formed segments. 
Table 3. 
Essentially the same as in No. 571, 
Externally 9 fully formed segments. Anterior segments roughly triangular in 
shape, have a distinctly formed cavity. 
Externally II segments. In anterior segments, the wall is partly broken down, 
mesenchyma replacing it. In both anterior and posterior segments, the cavity 
space is filled with cells, the segment nucleus. The posterior segments have 
a fairly distinct form which in cross section is somewhat quadrilateral. 
Condition essentially the same as in No. 619, Table 6. 
Anterior segments more differentiated. Cutis plate is distinct. Muscle plate 
not yet very clearly formed. Mesenchyma increased in amount. 16 segments 
(counted from sections). 
In the region of the heart, the myotome is now clearly formed. Cutis plate 
and muscle plate are distinct. Considerable mesenchyma around notochord 
and medullary tube. 23 segments (from sections; No. 565). 
In heart region, cutis plate and muscle plate of myotome are distinct. 29 seg- 
ments (from sections; No. 562). 
In heart region, cutis plate and muscle plate of myotome still distinct. Cells 
of muscle plate somewhat differentiated. About 32 segments (from sections; 
No. 559). 
In heart region, cutis plate and muscle plate of myotome still recognizable, 
but less distinct than at ı0!/, days. About 36 segments (from sections; No. 556). 
In anterior part of heart region, cutis plate and muscle plate of myotome still 
in part recognizable, but considerably modified, especially muscle plate. 
In region of segments, notochord anlage a thin bar not separated from ad- 
joining entoderm. This bar more distinct posterior to segments. Farther 
posterior, it is connected with mesoderm. 
Notochord anlage, a thin bar, not separated from entoderm in region of 
segments and anterior to them. Here mesoderm does not cross median line 
of body. Just anterior to primitive streak, this bar, larger, connects with 
mesoderm and is distinct from entoderm. 
Small notochord anlage not separated from entoderm in region of segments. 
Just anterior to primitive streak, anlage of notochord is connected with 
mesoderm and separated from entoderm. 
Essentially like No. 571, Table 3. 
Notochord anlage a thin bar not separated from entoderm except just anterior 
to primitive streak. This bar merges into region of primitive streak. 
| 
| 
In heart region, notochord anlage is a small number of cells connected with, 
entoderm of dorsal wall of fore-gut and in contact with medullary tube. In| 
region of segments, notochord anlage a small bar partly connected with 
entoderm. Posteriorly, this bar merges into region of primitive streak. 
Essentially like No. 619, Table 6. 
Notochord anlage, dorsal to anterior part of fore-gut, a transversely narrow 
bar of cells joined to entoderm and touching medullary tube. Notochord anlage | 
merges into region of remnant of primitive streak. 
Posterior to ear, notochord a transversely narrow bar of cells joined to ento- 
derm of fore-gut. In heart region, notochord separated from entoderm by 
mesenchyma. Posteriorly, dorsal to hind-gut, notochord joined to entoderm. 
Farther caudad, notochord anlage distinct from entoderm. In trunk, notochord 
separated from entoderm of gut by dorsal aorta. 
I 
Anterior to ear, notochord a bar of cells, transversely very narrow, attached | 
to entoderm of pharynx, not to hind-brain. In trunk, notochord small, circular 
in cross section, imbedded in mesenchyma. Near tip of tail, notochord, me- 
dullary tube and gut fuse into mass of cells joined to mesoderm. | 
A clear connection between notochord and hypophysis. In head and trunk, 
notochord small, nearly circular in cross section, imbedded in mesenchyma. 
Notochord, medullary tube and post-anal gut fuse in tip of tail into a mass of 
cells not separated from mesoderm. 
| 
Distinct connection betwen notochord and hypophysis. Notochord imbedded 
in mesenchyma extends from hypophysis to tip of tail. In heart region, first 
indication of notochordal sheath. Notochord, medullary tube and post-anal 
gut fuse in tip of tail into common cell mass. 
| 
Apparently no connection between notochord and hypophysis. Notochord | 
small, circular in cross section, imbedded in mesenchyma. In heart region, | 
shight indication of notochordal sheath. Slender connection between notochord 
and hypophysis in sagittal series. 
Apparently no connection between notochord and hypophysis. Indication of 
notochordal sheath in region of anterior limb buds. Notochord, medullary tube 
and post-anal gut fuse in tip of tail. 
